three.js/test/unit/src/math/Math.js

/**
 * @author humbletim / https://github.com/humbletim
 */

QUnit.module( "Math" );

//https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sign
//http://people.mozilla.org/~jorendorff/es6-draft.html#sec-math.sign
/* 
20.2.2.29 Math.sign(x)

Returns the sign of the x, indicating whether x is positive, negative or zero.

If x is NaN, the result is NaN.
If x is -0, the result is -0.
If x is +0, the result is +0.
If x is negative and not -0, the result is -1.
If x is positive and not +0, the result is +1.
*/

QUnit.test( "Math.sign/polyfill", function( assert ) {

	assert.ok( isNaN( Math.sign(NaN) ) , "If x is NaN<NaN>, the result is NaN.");
	assert.ok( isNaN( Math.sign(new THREE.Vector3()) ) , "If x is NaN<object>, the result is NaN.");
	assert.ok( isNaN( Math.sign() ) , "If x is NaN<undefined>, the result is NaN.");
	assert.ok( isNaN( Math.sign('--3') ) , "If x is NaN<'--3'>, the result is NaN.");
	assert.ok( isNegativeZero( Math.sign(-0) ) , "If x is -0, the result is -0.");
	assert.ok( Math.sign(+0) === +0 , "If x is +0, the result is +0.");
	assert.ok( Math.sign(-Infinity) === -1 , "If x is negative<-Infinity> and not -0, the result is -1.");
	assert.ok( Math.sign('-3') === -1 , "If x is negative<'-3'> and not -0, the result is -1.");
	assert.ok( Math.sign('-1e-10') === -1 , "If x is negative<'-1e-10'> and not -0, the result is -1.");
	assert.ok( Math.sign(+Infinity) === +1 , "If x is positive<+Infinity> and not +0, the result is +1.");
	assert.ok( Math.sign('+3') === +1 , "If x is positive<'+3'> and not +0, the result is +1.");

	// Comparing with -0 is tricky because 0 === -0. But
	// luckily 1 / -0 === -Infinity so we can use that.

	function isNegativeZero( value ) {

		return value === 0 && 1 / value < 0;

	}

});