The if
statement executes a statement if a specified condition is truthy. If the condition is falsy, another statement can be executed.
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Syntax
if (condition) statement1 [else statement2]
condition
- An expression that is considered to be either truthy or falsy.
statement1
- Statement that is executed if
condition
is truthy. Can be any statement, including further nestedif
statements. To execute multiple statements, use a block statement ({ ... }
) to group those statements. To execute no statements, use an empty statement. statement2
- Statement that is executed if
condition
is falsy and theelse
clause exists. Can be any statement, including block statements and further nestedif
statements.
Description
Multiple if...else
statements can be nested to create an else if
clause. Note that there is no elseif
(in one word) keyword in JavaScript.
if (condition1)
statement1
else if (condition2)
statement2
else if (condition3)
statement3
...
else
statementN
To see how this works, this is how it would look if the nesting were properly indented:
if (condition1)
statement1
else
if (condition2)
statement2
else
if (condition3)
...
To execute multiple statements within a clause, use a block statement ({ ... }
) to group those statements. In general, it is a good practice to always use block statements, especially in code involving nested if
statements:
if (condition) {
statements1
} else {
statements2
}
Do not confuse the primitive Boolean values true
and false
with truthiness or falsiness of the Boolean
object. Any value that is not false
, undefined
, null
, 0
, -0
, NaN
, or the empty string (""
), and any object, including a Boolean object whose value is false
, is considered truthy when used as the condition. For example:
var b = new Boolean(false);
if (b) // this condition is truthy
Examples
Using if...else
if (cipher_char === from_char) {
result = result + to_char;
x++;
} else {
result = result + clear_char;
}
Using else if
Note that there is no elseif
syntax in JavaScript. However, you can write it with a space between else
and if
:
if (x > 50) {
/* do something */
} else if (x > 5) {
/* do something */
} else {
/* do something */
}
Assignment within the conditional expression
It is advisable to not use simple assignments in a conditional expression, because the assignment can be confused with equality when glancing over the code. For example, do not use the following code:
if (x = y) {
/* do something */
}
If you need to use an assignment in a conditional expression, a common practice is to put additional parentheses around the assignment. For example:
if ((x = y)) {
/* do something */
}
Specifications
Specification |
---|
ECMAScript (ECMA-262)The definition of 'if statement' in that specification. |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Update compatibility data on GitHub
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
if...else
|
Chrome
Full support 1 |
Edge
Full support 12 |
Firefox
Full support 1 |
IE
Full support 3 |
Opera
Full support 3 |
Safari
Full support 1 |
WebView Android
Full support 1 |
Chrome Android
Full support 18 |
Firefox Android
Full support 4 |
Opera Android
Full support 10.1 |
Safari iOS
Full support 1 |
Samsung Internet Android
Full support 1.0 |
nodejs
Full support 0.1.100 |
Legend
- Full support
- Full support
See also
if...else by Mozilla Contributors is licensed under CC-BY-SA 2.5.