Extension of ES6 value

1、 Binary and octal representations

ES6 Provides a new way to write binary and octal values , Use prefixes, respectively 0b（ or 0B） and 0o（ or 0O） Express .

console.log(0b111110111 === 503)//true
console.log(0o767 === 503)//true

from ES5 Start , In the strict model , Octal no longer allows prefixes 0 Express ,ES6 To be more specific , To use a prefix 0o Express .

Nonstrict mode

(function () {
    console.log(0o11 === 011);
})() //true

  Strict mode

(function(){
  'use strict';
  console.log(0o11 === 011);
})() // Uncaught SyntaxError: Octal literals are not allowed in strict mode.

If you want to 0b and 0o The string value of the prefix is converted to decimal , To use Number Method .

Number('0b111')  // 7
Number('0o10')  // 8

2、 Common expansion methods of numerical values

Reference to the method of numerical expansion ：http://caibaojian.com/es6/string.html

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

The difference from traditional methods is that there is no implicit conversion

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

2.2、ES6 Take a global approach parseInt() and parseFloat(), Migration to Number The above object , The behavior remains completely the same

// ES5 Writing 
parseInt('12.34') // 12
parseFloat('123.45#') // 123.45

// ES6 Writing 
Number.parseInt('12.34') // 12
Number.parseFloat('123.45#') // 123.45

The purpose of this , Is to gradually reduce the overall approach , Make the language modular step by step

2.3、Number.isInteger() Used to determine whether a value is an integer

stay JavaScript Inside , Integers and floating-point numbers are stored in the same way , therefore 3 and 3.0 Be treated as the same value

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

3、Math Method extension

3.1、Math.trunc Method is used to remove the decimal part of a number , Returns the integer part , There will be implicit conversions

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

3.2、Math.sign Method is used to determine whether a number is positive 、 negative 、 It's still zero .

• The parameter is a positive number , return +1;
• The argument is negative , return -1;
• Parameter is 0, return 0;
• Parameter is -0, return -0;
• Other values , return NaN.

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