es6 Learning Notes - Extension of Numbers

There are some unused or unsupported ones that are not recorded. In general, this article is just a memo.

Number.isFinite(), Number.isNaN()

Number.isFinite() is used to check whether a value is finite.

console.log(Number.isFinite(15)); // true
console.log(Number.isFinite(0.8)); // true
console.log(Number.isFinite(NaN)); // false
console.log(Number.isFinite(Infinity)); // false
console.log(Number.isFinite(-Infinity)); // false
console.log(Number.isFinite('foo')); // False, the string is also false
console.log(Number.isFinite('15')); // false
console.log(Number.isFinite(true)); // False, Boolean value is also false

Number.isNaN() is used to check whether a value is NaN.

console.log(Number.isNaN(NaN)) // true
console.log(Number.isNaN(15)) // false
console.log(Number.isNaN('15')) // false
console.log(Number.isNaN(true)) // false
console.log(Number.isNaN(9/NaN)) // true
console.log(Number.isNaN('true'/0)) // true
console.log(Number.isNaN('true'/'true')) // true

The two new methods are only valid for numerical values, and all non-numerical methods return false.

parseInt() and parseFloat()

ES6 ports the global methods parseInt() and parseFloat() onto Number objects, and the behavior remains unchanged.

// The way to write ES5
parseInt('12.34') // 12
parseFloat('123.45#') // 123.45

// The way to write ES6
Number.parseInt('12.34') // 12

Number.isInteger()

Number.isInteger() is used to determine whether a value is an integer. It should be noted that within JavaScript, integers and floating-point numbers are stored in the same way, so 3 and 3.0 are considered to be the same value.

console.log(Number.isInteger(25)) // true
console.log(Number.isInteger(25.0)) // true
console.log(Number.isInteger(25.1)) // false
console.log(Number.isInteger("15")) // false
console.log(Number.isInteger(true)) // false

Number.EPSILON

• ES6 adds a minimal constant Number.EPSILON to the Number object to set an error range for floating-point computation.

• If this error can be less than Number.EPSILON, we can assume that the correct result has been obtained.

0.1 + 0.2
// 0.30000000000000004

0.1 + 0.2 - 0.3
// 5.551115123125783e-17

5.551115123125783e-17.toFixed(20)
// '0.00000000000000005551'// Infinitely close to 0

Number.EPSILON.toFixed(20)
// '0.00000000000000022204'// / As long as it's smaller than that, we think he's right.


function withinErrorMargin (left, right) {
    return Math.abs(left - right) < Number.EPSILON;
}
console.log(withinErrorMargin(0.1 + 0.2, 0.3))
// true
console.log(withinErrorMargin(0.2 + 0.2, 0.3))
// false

Security integers and Number.isSafeInteger()

JavaScript can accurately represent integers ranging from - 2 ^ 53 to 2 ^ 53 (excluding two endpoints), beyond which the value cannot be accurately represented.

console.log(Math.pow(2, 53)); // 9007199254740992
console.log(Number.MAX_SAFE_INTEGER === Math.pow(2, 53) + 1)//false
console.log(Number.MAX_SAFE_INTEGER === Math.pow(2, 53) - 1) //true, equal to a number less than 1 than the maximum range

Similarly, Number.MAX_SAFE_INTEGER can be used for reference.

Number.isSafeInteger() is used to determine whether an integer falls within this range.

console.log(Number.isSafeInteger(Number.MIN_SAFE_INTEGER - 1)) // false
console.log(Number.isSafeInteger(Number.MIN_SAFE_INTEGER)) // true
console.log(Number.isSafeInteger(Number.MAX_SAFE_INTEGER)) // true
console.log(Number.isSafeInteger(Number.MAX_SAFE_INTEGER + 1)) // false

Extension of Math Objects

Math.trunc

The Math.trunc method is used to remove the decimal part of a number and return the integer part.

console.log(Math.trunc(4.1)) // 4
console.log(Math.trunc(4.9)) // 4
console.log(Math.trunc(-4.1)) // -4
console.log(Math.trunc(-4.9)) // -4
console.log(Math.trunc(-0.1234)) // -0

Math.sign()

Math.sign method is used to determine whether a number is positive, negative or zero.

console.log(Math.sign(-5)) // -1
console.log(Math.sign(5)) // 1
console.log(Math.sign(0)) // 0
console.log(Math.sign(-0)) // -0
console.log(Math.sign(NaN)) // NaN
console.log(Math.sign('foo')); // NaN
console.log(Math.sign());      // NaN

Reference:

1. Numerical expansion of es6