Assignment Operators
Introduction to JavaScript assignment operators
An assignment operator (=) assigns a value to a variable. The syntax of the assignment operator is as follows:
let a = b;
In this syntax, JavaScript evaluates the expression b first and assigns the result to the variable a.
The following example declares the counter variable and initializes its value to zero:
let counter = 0;
The following example increases the counter variable by one and assigns the result to the counter variable:
let counter = 0;
counter = counter + 1;
When evaluating the second statement, JavaScript evaluates the expression on the right-hand first (counter + 1) and assigns the result to the counter variable. After the second assignment, the counter variable is 1.
To make the code more concise, you can use the += operator like this:
let counter = 0;
counter += 1;
In this syntax, you don’t have to repeat the counter variable twice in the assignment.
The following table illustrates assignment operators that are shorthand for another operator and the assignment:
| Operator | Meaning | Description |
|---|---|---|
| a = b | a = b | Assigns the value of b to a. |
| a += b | a = a + b | Assigns the result of a plus b to a. |
| a -= b | a = a – b | Assigns the result of a minus b to a. |
| a *= b | a = a * b | Assigns the result of a times b to a. |
| a /= b | a = a / b | Assigns the result of a divided by b to a. |
| a %= b | a = a % b | Assigns the result of a modulo b to a. |
| a &=b | a = a & b | Assigns the result of a AND b to a. |
| a | =b | a = a |
| a ^=b | a = a ^ b | Assigns the result of a XOR b to a. |
| a <<= b | a = a << b | Assigns the result of a shifted left by b to a. |
| a >>= b | a = a >> b | Assigns the result of a shifted right (sign preserved) by b to a. |
| a >>>= b | a = a >>> b | Assigns the result of a shifted right by b to a. |
Chaining JavaScript assignment operators
If you want to assign a single value to multiple variables, you can chain the assignment operators. For example:
let a = 10, b = 20, c = 30;
a = b = c;// all variables are 30
In this example, JavaScript evaluates from right to left. Therefore, it does the following:
let a = 10, b = 20, c = 30;
b = c;// b is 30
a = b;// a is also 30
Summary
- Use the assignment operator (
=) to assign a value to a variable. - Chain the assignment operators if you want to assign a single value to multiple variables.