The if
statement executes a statement if a specified condition is truthy. If the condition is falsy, another statement can be executed.
if...else
Try it
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 nested
if
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 */ }
Using an assignment as a condition
You should almost never have an if...else
with an assignment like "x = y
" as a condition:
if (x = y) { /* do something */ }
However, in the rare case you find yourself wanting to do something like that, the while
documentation has a Using an assignment as a condition section with an example showing a general best-practice syntax you should know about and follow.
Specifications
Specification |
---|
ECMAScript Language Specification # sec-if-statement |
Browser compatibility
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | Deno | Node.js | |
if...else |
1
|
12
|
1
|
3
|
3
|
1
|
1
|
18
|
4
|
10.1
|
1
|
1.0
|
1.0
|
0.10.0
|
See also
© 2005–2022 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/if...else