The Math.imul() function returns the result of the C-like 32-bit multiplication of the two parameters.


Math.imul(a, b)


First number.
Second number.

Return value

The result of the C-like 32-bit multiplication of the given arguments.


Math.imul() allows for 32-bit integer multiplication with C-like semantics. This feature is useful for projects like Emscripten. Because imul() is a static method of Math, you always use it as Math.imul(), rather than as a method of a Math object you created (Math is not a constructor). If you use normal JavaScript floating point numbers in imul, you will experience a degrade in performance. This is because of the costly conversion from a floating point to an integer for multiplication, and then converting the multiplied integer back into a floating point. The reason imul exists is because it is faster in only one (so far) circumstance: AsmJS. AsmJS allows for JIST-optimizers to more easily implement internal integers in JavaScript. Multiplying two numbers stored internally as integers (which is only possible with AsmJS) with imul is the only potential circumstance where Math.imul may prove performant in current browsers.


Using Math.imul()

Math.imul(2, 4);          // 8
Math.imul(-1, 8);         // -8
Math.imul(-2, -2);        // 4
Math.imul(0xffffffff, 5); // -5
Math.imul(0xfffffffe, 5); // -10


This can be emulated with the following function:

Math.imul = Math.imul || function(a, b) {
  var ah = (a >>> 16) & 0xffff;
  var al = a & 0xffff;
  var bh = (b >>> 16) & 0xffff;
  var bl = b & 0xffff;
  // the shift by 0 fixes the sign on the high part
  // the final |0 converts the unsigned value into a signed value
  return ((al * bl) + (((ah * bl + al * bh) << 16) >>> 0)|0);


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

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic Support28 (Yes)20 No167
FeatureAndroidChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic Support (Yes) (Yes) (Yes)20 No (Yes)7

Document Tags and Contributors

 Last updated by: Rsperberg,