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This article covers features introduced in SpiderMonkey 1.8.1

Determines if two jsvals are the same, as determined by the SameValue algorithm in ECMAScript 262, 5th edition.

SameValue slightly differs from strict equality (===) in that +0 and -0 are not the same and in that NaN is the same as NaN. The SameValue algorithm is equivalent to the following JavaScript:

function SameValue(v1, v2)
  if (v1 === 0 && v2 === 0)
    return 1 / v1 === 1 / v2;
  if (v1 !== v1 && v2 !== v2)
    return true;
  return v1 === v2;


// Added in SpiderMonkey 45

JS_SameValue(JSContext *cx, JS::Handle<JS::Value> v1, JS::Handle<JS::Value> v2,
             bool *same);

// Obsolete since JSAPI 39

JS_SameValue(JSContext *cx, jsval v1, jsval v2, bool *same);
Name Type Description
cx JSContext * Pointer to a JS context from which to derive runtime information. Requires request. In a JS_THREADSAFE build, the caller must be in a request on this JSContext.
v1 JS::Handle<JS::Value> / jsval The first value.
v2 JS::Handle<JS::Value> / jsval The second value.


JS_SameValue determines whether two values are the same, returning true or false accordingly. This method is infallible.

See Also

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 Contributors to this page: arai, fscholz, kscarfone, ethertank
 Last updated by: arai,