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The Math.trunc() function returns the integer part of a number by removing any fractional digits.




A number.

Return value

The integer part of the given number.


Unlike the other three Math methods: Math.floor(), Math.ceil() and Math.round(), the way Math.trunc() works is very simple. It truncates (cuts off) the dot and the digits to the right of it, no matter whether the argument is a positive or negative number.

The argument passed to this method will be converted to number type implicitly.

Because trunc() is a static method of Math, you always use it as Math.trunc(), rather than as a method of a Math object you created (Math is not a constructor).


Using Math.trunc()

Math.trunc(13.37);    // 13
Math.trunc(42.84);    // 42
Math.trunc(0.123);    //  0
Math.trunc(-0.123);   // -0
Math.trunc('-1.123'); // -1
Math.trunc(NaN);      // NaN
Math.trunc('foo');    // NaN
Math.trunc();         // NaN


if (!Math.trunc) {
	Math.trunc = function(v) {
		v = +v;
		if (!isFinite(v)) return v;
		return (v - v % 1)   ||   (v < 0 ? -0 : v === 0 ? v : 0);
		// returns:
		//  0        ->  0
		// -0        -> -0
		//  0.2      ->  0
		// -0.2      -> -0
		//  0.7      ->  0
		// -0.7      -> -0
		//  Infinity ->  Infinity
		// -Infinity -> -Infinity
		//  NaN      ->  NaN
		//  null     ->  0


if (!Math.trunc) {
	Math.trunc = function (v) {
		return v < 0 ? Math.ceil(v) : Math.floor(v);


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Math.trunc' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of 'Math.trunc' in that specification.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
truncChrome Full support 38Edge Full support 12Firefox Full support 25IE No support NoOpera Full support 25Safari Full support 8WebView Android Full support YesChrome Android Full support YesFirefox Android Full support 25Opera Android Full support YesSafari iOS Full support 8Samsung Internet Android Full support Yesnodejs Full support 0.12


Full support  
Full support
No support  
No support

See also

Document Tags and Contributors

Cập nhật lần cuối bởi: Andrew-Cottrell,