. [ Deprecated features ](/en-US/docs/Web/JavaScript/Reference/Deprecated_and_obsolete_features)

##  In this article

  * Try it 
  * Syntax 
  * Description 
  * Examples 
  * Specifications 
  * Browser compatibility 
  * See also 

#  Subtraction assignment (-=)

The **subtraction assignment (` -= ` ) ** operator performs [ subtraction
](/en-US/docs/Web/JavaScript/Reference/Operators/Subtraction) on the two
operands and assigns the result to the left operand.

##  Try it

##  Syntax

js

    
    
    x -= y
    

##  Description

` x -= y ` is equivalent to ` x = x - y ` , except that the expression ` x `
is only evaluated once.

##  Examples

###  Using subtraction assignment

js

    
    
    let bar = 5;
    
    bar -= 2; // 3
    bar -= "foo"; // NaN
    
    let foo = 3n;
    foo -= 2n; // 1n
    

##  Specifications

Specification  
---  
[ ECMAScript Language Specification  
#  sec-assignment-operators  ](https://tc39.es/ecma262/multipage/ecmascript-
language-expressions.html#sec-assignment-operators)  
  
##  Browser compatibility

BCD tables only load in the browser  with JavaScript enabled. Enable
JavaScript to view data.

##  See also

  * [ Assignment operators in the JS guide ](/en-US/docs/Web/JavaScript/Guide/Expressions_and_operators#assignment_operators)
  * [ Subtraction ( ` - ` ) ](/en-US/docs/Web/JavaScript/Reference/Operators/Subtraction)

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