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Home » Top 3 Practical Ways to Perform Javascript String Concatenation

Top 3 Practical Ways to Perform Javascript String Concatenation

Summary : in this tutorial, you’ll learn how to concatenate strings in JavaScript.

JavaScript provides various options that allow you to concatenate two or more strings:

• Use the concat() method
• Use the + and += operators
• Use the template literals

1) Using the concat() method

The String.prototype.concat() concatenates two or more string arguments and returns a new string:

The concat() accepts a varied number of string arguments and returns a new string containing the combined string arguments.

If you pass non-string arguments into the concat() , it will convert these arguments to a string before concatenating. For example:

This example concatenates strings into a new string:

The following example concatenates all string elements in an array into a string:

2) Using the + and += operators

The operator + allows you to concatenate two strings. For example:

To compose a string piece by piece, you use the += operator:

According to a performance test on some modern web browsers, the + and += operators perform faster than the concat() method.

3) Using template literals

ES6 introduces the template literals that allow you to perform string interpolation.

The following example shows how to concatenate three strings:

In this tutorial, you have learned how to concatenate strings in JavaScript using the concat() method, + and += operator, and template literals.

3 Ways to Concatenate Strings in JavaScript

There are 3 ways to concatenate strings in JavaScript. In this tutorial, you'll the different ways and the tradeoffs between them.

The + Operator

The same + operator you use for adding two numbers can be used to concatenate two strings.

You can also use += , where a += b is a shorthand for a = a + b .

If the left hand side of the + operator is a string, JavaScript will coerce the right hand side to a string. That means it is safe to concatenate objects, numbers, null , and undefined .

The + and += operators are fast on modern JavaScript engines , so no need to worry about something like Java's StringBuilder class .

Array#join()

The Array#join() function creates a new string from concatenating all elements in an array. For example:

The first parameter to join() is called the separator . By default, the separator is a single comma ',' .

You can pass in any separator you want. Separators make Array#join() the preferred choice for concatenating strings if you find yourself repeating the same character over and over again. For example, you can use ' ' as the separator to join an array of words:

Or you can use '/' to join together URL fragments:

Separators make Array#join() a very flexible way to concatenate strings. If you want to join together a variable number of strings, you should generally use join() rather than a for loop with + .

String#concat()

JavaScript strings have a built-in concat() method . The concat() function takes one or more parameters, and returns the modified string. Strings in JavaScript are immutable, so concat() doesn't modify the string in place.

The downside of using concat() is that you must be certain str1 is a string. You can pass non-string parameters to concat() , but you will get a TypeError if str == null .

The concat() function is rarely used because it has more error cases than the + operator. For example, you would get unexpected behavior if you call concat() on a value that happens to be an array . You should use + instead of concat() unless you have a very good reason.

If you must use concat() , it is usually best to call it on an empty string:

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How to Join/Concatenate Strings in JavaScript

• Introduction

Strings are one of the most common data types used in software - they represent strings of characters that we parse as words.

String concatenation is a pretty standard task, especially since we don't always deal with static strings. We often create strings dynamically, such as with ES6 Templates, or simply concatenate strings to form new ones.

If you'd like to read more about creating dynamic formatted strings - read our Guide to ES6 Templates/String Literals in Node.js !

In this tutorial, we'll take a look at how to join/append/concatenate strings in JavaScript.

Note: Strings are immutable , meaning they can't really be changed. Whenever you call a changing operation on a string, a copy is constructed with the changes applied and it's returned instead of the original one.

• Concatenate With the + Operator

The easiest, and probably most intuitive approach to string concatenation is using the + operator:

Running this short piece of code results in:

It is possible to assign a string in memory to a reference variable, and reference the object instead of concatenating it directly:

This also results in:

Note: In most cases, you can reasonably replace a = and + with the shorthand += , which lets you omit the reference to the first operand , which will be replaced with the variable you're assigning the result to.

Instead, you could be writing the short-hand version:

It's worth noting that other data types can be thrown into the mix as well, and whenever implicit conversion is possible - JavaScript will "match" the data types into strings.

For instance, integers are easily converted to strings so if you try concatenating an integer onto a string - the integer is converted before being appended. A string may not be converted into an integer at all times - such as when it doesn't represent a number or has odd formatting, so generally, it's easier to convert to a string, than from a string:

This results in both the boolean and integer being converted into string representations and then appended to the "hello" string:

• String.prototype.concat()

The concat() method was created specifically for this task - to concatenate strings. It can be invoked over any string, and accepts another string to be concatenated to the calling one.

In a sense, it's similar to using the short-hand += operator:

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This results in:

Additionally, you can specify a delimiter as the first argument, which is then added in-between all of the concatenated strings:

• Array.prototype.join()

The join() method of the Array class is used to join the elements of an array into a string, with a default delimiter of a comma ( , ).

This allows us to deal with a larger number of strings in a much more concise way, and it's not unheard of to read a file into an array, or to work with an array of strings you'd like to join together.

If you don't pass in any arguments into the method - the default value will be used to delimit the newly joined strings. Let's pass in an empty string to skip that and just join them similar to what we've seen before:

• Which Approach to Use?

It's advised to prefer the concat() function instead of the + operator , due to performance benefits. However, this doesn't actually always hold and takes in several assumptions into mind.

First of all - the number of strings you're concatenating plays a role in this, as well as other factors you might not even be aware of. Let's benchmark the concat() method as well as the + operator:

But wait, let's switch the environment and run this on a different machine:

And let's run that on the same machine again:

The execution times vary wildly (although, all of them are acceptable in speed). It's also worth noting the official statement from MDN , regarding the performance benefits:

It is strongly recommended that the assignment operators (+, +=) are used instead of the concat() method.

Which might seem odd, given the fact that concat() outperforms the operators in the tests or at worst is the same speed. What gives? Well, benchmarking code like this isn't as easy as simply running it and observing the results.

Your browser, its version, as well as the optimizer it uses may vary from machine to machine, and properties like those really impact the performance. For instance, we've used different strings in the concatenation, the ones generated from iteration. If we were to use the same string, an optimizer such as Google's V8 would further optimize the usage of the string.

Test and verify your own code instead of taking advice at face value. Not all machines and environments are the same, and what works great on one, might not work great on another. Take this into consideration when creating applications as well.

We've taken a look at how to concatenate strings in JavaScript using the + operator, the join() method of the Arrays class as well as the concat() method of the String class.

We've taken a look at the official stance and ran our own tests to see which approach is the most performant - and as usual, it depends on various factors.

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• Assignment operators

An assignment operator assigns a value to its left operand based on the value of its right operand.

The basic assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x . The other assignment operators are usually shorthand for standard operations, as shown in the following definitions and examples.

Simple assignment operator which assigns a value to a variable. The assignment operation evaluates to the assigned value. Chaining the assignment operator is possible in order to assign a single value to multiple variables. See the example.

Addition assignment

The addition assignment operator adds the value of the right operand to a variable and assigns the result to the variable. The types of the two operands determine the behavior of the addition assignment operator. Addition or concatenation is possible. See the addition operator for more details.

Subtraction assignment

The subtraction assignment operator subtracts the value of the right operand from a variable and assigns the result to the variable. See the subtraction operator for more details.

Multiplication assignment

The multiplication assignment operator multiplies a variable by the value of the right operand and assigns the result to the variable. See the multiplication operator for more details.

Division assignment

The division assignment operator divides a variable by the value of the right operand and assigns the result to the variable. See the division operator for more details.

Remainder assignment

The remainder assignment operator divides a variable by the value of the right operand and assigns the remainder to the variable. See the remainder operator for more details.

Exponentiation assignment

This is an experimental technology, part of the ECMAScript 2016 (ES7) proposal. Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future version of browsers as the spec changes.

The exponentiation assignment operator evaluates to the result of raising first operand to the power second operand. See the exponentiation operator for more details.

Left shift assignment

The left shift assignment operator moves the specified amount of bits to the left and assigns the result to the variable. See the left shift operator for more details.

Right shift assignment

The right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the right shift operator for more details.

Unsigned right shift assignment

The unsigned right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the unsigned right shift operator for more details.

Bitwise AND assignment

The bitwise AND assignment operator uses the binary representation of both operands, does a bitwise AND operation on them and assigns the result to the variable. See the bitwise AND operator for more details.

Bitwise XOR assignment

The bitwise XOR assignment operator uses the binary representation of both operands, does a bitwise XOR operation on them and assigns the result to the variable. See the bitwise XOR operator for more details.

Bitwise OR assignment

The bitwise OR assignment operator uses the binary representation of both operands, does a bitwise OR operation on them and assigns the result to the variable. See the bitwise OR operator for more details.

Left operand with another assignment operator

In unusual situations, the assignment operator (e.g. x += y ) is not identical to the meaning expression (here x = x + y ). When the left operand of an assignment operator itself contains an assignment operator, the left operand is evaluated only once. For example:

Specifications

Browser compatibility.

• Arithmetic operators

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JAVASCRIPT ASSIGNMENT OPERATORS

In this tutorial, you will learn about all the different assignment operators in javascript and how to use them in javascript.

Assignment Operators

In javascript, there are 16 different assignment operators that are used to assign value to the variable. It is shorthand of other operators which is recommended to use.

The assignment operators are used to assign value based on the right operand to its left operand.

The left operand must be a variable while the right operand may be a variable, number, boolean, string, expression, object, or combination of any other.

One of the most basic assignment operators is equal = , which is used to directly assign a value.

Assignment Operators List

Here is the list of all assignment operators in JavaScript:

In the following table if variable a is not defined then assume it to be 10.

Assignment operator

The assignment operator = is the simplest value assigning operator which assigns a given value to a variable.

The assignment operators support chaining, which means you can assign a single value in multiple variables in a single line.

Addition assignment operator

The addition assignment operator += is used to add the value of the right operand to the value of the left operand and assigns the result to the left operand.

On the basis of the data type of variable, the addition assignment operator may add or concatenate the variables.

Subtraction assignment operator

The subtraction assignment operator -= subtracts the value of the right operand from the value of the left operand and assigns the result to the left operand.

If the value can not be subtracted then it results in a NaN .

Multiplication assignment operator

The multiplication assignment operator *= assigns the result to the left operand after multiplying values of the left and right operand.

Division assignment operator

The division assignment operator /= divides the value of the left operand by the value of the right operand and assigns the result to the left operand.

Remainder assignment operator

The remainder assignment operator %= assigns the remainder to the left operand after dividing the value of the left operand by the value of the right operand.

Exponentiation assignment operator

The exponential assignment operator **= assigns the result of exponentiation to the left operand after exponentiating the value of the left operand by the value of the right operand.

Left shift assignment

The left shift assignment operator <<= assigns the result of the left shift to the left operand after shifting the value of the left operand by the value of the right operand.

Right shift assignment

The right shift assignment operator >>= assigns the result of the right shift to the left operand after shifting the value of the left operand by the value of the right operand.

Unsigned right shift assignment

The unsigned right shift assignment operator >>>= assigns the result of the unsigned right shift to the left operand after shifting the value of the left operand by the value of the right operand.

Bitwise AND assignment

The bitwise AND assignment operator &= assigns the result of bitwise AND to the left operand after ANDing the value of the left operand by the value of the right operand.

Bitwise OR assignment

The bitwise OR assignment operator |= assigns the result of bitwise OR to the left operand after ORing the value of left operand by the value of the right operand.

Bitwise XOR assignment

The bitwise XOR assignment operator ^= assigns the result of bitwise XOR to the left operand after XORing the value of the left operand by the value of the right operand.

Logical AND assignment

The logical AND assignment operator &&= assigns value to left operand only when it is truthy .

Note : A truthy value is a value that is considered true when encountered in a boolean context.

Logical OR assignment

The logical OR assignment operator ||= assigns value to left operand only when it is falsy .

Note : A falsy value is a value that is considered false when encountered in a boolean context.

Logical nullish assignment

The logical nullish assignment operator ??= assigns value to left operand only when it is nullish ( null or undefined ).

4 ways to concatenate strings in JavaScript

Concat() method, the + operator, template literals, join() method.

String concatenation is a common task in any programming language. There are 4 ways to combine strings in JavaScript.

In this article, we'll look at all these methods to perform string concatenation in JavaScript.

JavaScript String object has a built-in concat() method. As the name suggests, this method joins or merges two or more strings.

The concat() method doesn't modify the string in place. Instead, it creates and returns a new string containing the text of the joined strings.

If the parameters are not of the type string, they are automatically converted to string values before concatenating.

The same + operator that we used to add two numbers can also be used to combine two strings:

The above method creates a brand new string. To mutate the existing string, you could use the shorthand += operator:

The assignment operators ( + , += ) perform faster on modern JavaScript engines, so there is no need to use the concat() method.

However, if you prefer readability over performance, use template literals (explained below).

Template literals provides a modern way to work with strings in JavaScript. They are primarily string literals with embedded expressions. You can use string interpolation, multi-line strings , and tagged expressions with them.

I personally use template literals in JavaScript (and even in Node.js) to combine strings. Because they're more readable with no awkward backslashes to escape quotes, no empty spaces, and no more plus operators. You write exactly how you want your string to appear.

The join() method concatenates all elements in an array and returns a new string:

The first parameter of the join() method is the separator. If skipped, a comma ( , ) is used as a default separator:

You can pass in any separator you want to combine strings:

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Assignment operators assign values to JavaScript variables.

Shift Assignment Operators

Bitwise assignment operators, logical assignment operators, the = operator.

The Simple Assignment Operator assigns a value to a variable.

Simple Assignment Examples

The += operator.

The Addition Assignment Operator adds a value to a variable.

Addition Assignment Examples

The -= operator.

The Subtraction Assignment Operator subtracts a value from a variable.

Subtraction Assignment Example

The *= operator.

The Multiplication Assignment Operator multiplies a variable.

Multiplication Assignment Example

The **= operator.

The Exponentiation Assignment Operator raises a variable to the power of the operand.

Exponentiation Assignment Example

The /= operator.

The Division Assignment Operator divides a variable.

Division Assignment Example

The %= operator.

The Remainder Assignment Operator assigns a remainder to a variable.

Remainder Assignment Example

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The <<= Operator

The Left Shift Assignment Operator left shifts a variable.

Left Shift Assignment Example

The >>= operator.

The Right Shift Assignment Operator right shifts a variable (signed).

Right Shift Assignment Example

The >>>= operator.

The Unsigned Right Shift Assignment Operator right shifts a variable (unsigned).

Unsigned Right Shift Assignment Example

The &= operator.

The Bitwise AND Assignment Operator does a bitwise AND operation on two operands and assigns the result to the the variable.

Bitwise AND Assignment Example

The |= operator.

The Bitwise OR Assignment Operator does a bitwise OR operation on two operands and assigns the result to the variable.

Bitwise OR Assignment Example

The ^= operator.

The Bitwise XOR Assignment Operator does a bitwise XOR operation on two operands and assigns the result to the variable.

Bitwise XOR Assignment Example

The &&= operator.

The Logical AND assignment operator is used between two values.

If the first value is true, the second value is assigned.

Logical AND Assignment Example

The &&= operator is an ES2020 feature .

The ||= Operator

The Logical OR assignment operator is used between two values.

If the first value is false, the second value is assigned.

Logical OR Assignment Example

The ||= operator is an ES2020 feature .

The ??= Operator

The Nullish coalescing assignment operator is used between two values.

If the first value is undefined or null, the second value is assigned.

Nullish Coalescing Assignment Example

The ??= operator is an ES2020 feature .

Test Yourself With Exercises

Use the correct assignment operator that will result in x being 15 (same as x = x + y ).

Start the Exercise

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• JavaScript Set Reference
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• JavaScript BigInt
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• JavaScript this Keyword
• Strict mode in JavaScript
• Introduction to ES6
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JavaScript Exercises

• JavaScript Exercises, Practice Questions and Solutions

JavaScript operators are symbols used to operate the operands. Operators are used to perform specific mathematical and logical computations on operands.

JavaScript Operators: There are various operators supported by JavaScript.

Table of Content

JavaScript Ternary Operators

Javascript comma operators, javascript relational operators, javascript bigint operators.

JavaScript Arithmetic Operators perform arithmetic operations: addition (+), subtraction (-), multiplication (*), division (/), modulus (%), and exponentiation (**).

The assignment operation evaluates the assigned value. Chaining the assignment operator is possible in order to assign a single value to multiple variables

Comparison operators are mainly used to perform the logical operations that determine the equality or difference between the values.

JavaScript Logical Operators perform logical operations: AND (&&), OR (||), and NOT (!), evaluating expressions and returning boolean values.

The bitwise operator in JavaScript is used to convert the number to a 32-bit binary number and perform the bitwise operation. The number is converted back to the 64-bit number after the result. 

The ternary operator has three operands. It is the simplified operator of if/else.

Comma Operator (,)  mainly evaluates its operands from left to right sequentially and returns the value of the rightmost operand. 

A unary operation is an operation with only one operand.

JavaScript  Relational operators  are used to compare its operands and determine the relationship between them. They return a Boolean value (true or false) based on the comparison result.

JavaScript BigInt operators support arithmetic operations on BigInt data type, including addition, subtraction, multiplication, division, and exponentiation. Most operators that can be used between numbers can be used between  BigInt values as well.

JavaScript String Operators include concatenation (+) and concatenation assignment (+=), used to join strings or combine strings with other data types.

We have a list of JavaScript Operators reference where you can know more about these operators.

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