What is += in Javascript?

Question

For example, in the while loop:

while (i < 10) {
    text += "The number is " + i;
    i++;
}

What does it do? Thanks.

Answer 1

It is the addition assignment operator (+=) to add a value to a variable.

Depending of the current type of the defined value on a variable, it will read the current value add/concat another value into it and define on the same variable.

For a string, you concat the current value with another value

let name = "User";

name += "Name"; // name = "UserName";
name += " is ok"; // name = "UserName is ok";

It is the same:

var name = "User";

name = name + "Name"; // name = "UserName";
name = name + " is ok"; // name = "UserName is ok";

For numbers, it will sum the value:

let n = 3;

n += 2; // n = 5
n += 3; // n = 8

In Javascript, we also have the following expressions:

• -= - Subtraction assignment;

• /= - Division assignment;

• *= - Multiplication assignment;

• %= - Modulus (Division Remainder) assignment.

Answer 2

text += "The number is " + i;

is equivalent to

text = text + "The number is " + i;