if...else
BaselineWidely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
Theif...else
statement executes a statement if a specified condition istruthy. If the condition isfalsy, another statement in the optionalelse
clause will be executed.
Try it
function testNum(a) { let result; if (a > 0) { result = "positive"; } else { result = "NOT positive"; } return result;}console.log(testNum(-5));// Expected output: "NOT positive"
Syntax
if (condition) statement1// With an else clauseif (condition) statement1else statement2
condition
An expression that is considered to be eithertruthy orfalsy.
statement1
Statement that is executed ifcondition istruthy. Can be any statement, including further nested
if
statements. To execute multiple statements, use ablock statement ({ /* ... */ }
) to group those statements. To execute no statements, use anempty statement.statement2
Statement that is executed if
condition
isfalsy and theelse
clause exists. Can be any statement, including block statements and further nestedif
statements.
Description
Multipleif...else
statements can be nested to create anelse if
clause. Note that there is noelseif
(in one word) keyword in JavaScript.
if (condition1) statement1else if (condition2) statement2else if (condition3) statement3// …else statementN
To see how this works, this is how it would look if the nesting were properly indented:
if (condition1) statement1else if (condition2) statement2 else if (condition3) statement3// …
To execute multiple statements within a clause, use a block statement ({ /* ... */ }
) to group those statements.
if (condition) { statements1} else { statements2}
Not using blocks may lead to confusing behavior, especially if the code is hand-formatted. For example:
function checkValue(a, b) { if (a === 1) if (b === 2) console.log("a is 1 and b is 2"); else console.log("a is not 1");}
This code looks innocent — however, executingcheckValue(1, 3)
will log "a is not 1". This is because in the case ofdangling else, theelse
clause will be connected to the closestif
clause. Therefore, the code above, with proper indentation, would look like:
function checkValue(a, b) { if (a === 1) if (b === 2) console.log("a is 1 and b is 2"); else console.log("a is not 1");}
In general, it is a good practice to always use block statements, especially in code involving nestedif
statements.
function checkValue(a, b) { if (a === 1) { if (b === 2) { console.log("a is 1 and b is 2"); } } else { console.log("a is not 1"); }}
Do not confuse the primitive Boolean valuestrue
andfalse
with truthiness or falsiness of theBoolean
object. Any value that is notfalse
,undefined
,null
,0
,-0
,NaN
, or the empty string (""
), and any object, including a Boolean object whose value isfalse
, is consideredtruthy when used as the condition. For example:
const b = new Boolean(false);if (b) { console.log("b is truthy"); // "b is truthy"}
Examples
Using if...else
if (cipherChar === fromChar) { result += toChar; x++;} else { result += clearChar;}
Using else if
Note that there is noelseif
syntax in JavaScript. However, you can write it with a space betweenelse
andif
:
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 anif...else
with an assignment likex = y
as a condition:
if ((x = y)) { // …}
Because unlikewhile
loops, the condition is only evaluated once, so the assignment is only performed once. The code above is equivalent to:
x = y;if (x) { // …}
Which is much clearer. However, in the rare case you find yourself wanting to do something like that, thewhile
documentation has aUsing an assignment as a condition section with our recommendations.
Specifications
Specification |
---|
ECMAScript® 2026 Language Specification # sec-if-statement |