New APIs for Math, Number, String, Array, and Object

Math

Math.trunc()

Take out the decimal part of a decimal and return the integer part

<code>Math.trunc(1.239);  //1
Math.trunc(-3,1415926);  //-2
Math.trunc(3.9);  //3</code>

For null values ​​and values ​​that cannot be intercepted as integers, return NaN

<code>Math.trunc("a");  //NaN
Math.trunc();  //NaN
Math.trunc(NaN);  //NaN</code>

Math.sign()

Judge positive number, negative number or 0, return 1 for positive number, -1 for negative number, 0 for 0 and NaN for other values

<code>Math.sign(11.22);  //1
Math.sign(253);  //1
Math.sign(0);  //0
Math.sign(0.0);  //0
Math.sign(-0.0);  //-0
Math.sign(-0);  //-0
Math.sign(-345);  //-1
Math.sign(-2.983958);  //-1
Math.sign('a');  //NaN
Math.sign();  //NaN
Math.sign(NaN);  //NaN</code>

Math.cbrt()

Calculate the cube root of a number and return NaN for other values

<code>Math.cbrt(8);  //2
Math.cbrt(-64);  //-4
Math.cbrt(-27);//3
Math.sign('a');  //NaN</code>

Number.isInteger()

Determine whether a value is an integer. It returns true or it returns false

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

Number.isNaN()

Used to check whether a value is NaN

<code>Number.isNaN(NaN) // true  
Number.isNaN(15) // false  
Number.isNaN('15') // false  
Number.isNaN(true) // false </code>

String

includes()

Used to check whether any connected items in the array are included. If true is included, false is not included

<code>var str="weirenshi";
str.includes("shi")//ture
str.includes("ei")//ture
str.includes("df")//false
str.includes("dfghjk")//false</code>

startsWidth()

Starting with a string letter (one or two) returns true instead of false

<code>var str="weirenshi";
str.startsWidth("w")//ture
str.startsWidth("we")//ture
str.startsWidth("d")//false</code>

endsWidth

Ending with a string letter (one or two) returns true and does not contain false

<code>var str="weirenshi";
str.endsWidth("i")//ture
str.endsWidth("hi")//ture
str.endsWidth("d")//false</code>

repeat

Copy: Define as many as you want and you will copy as many as you want

<code>"abc".repeat(3) // "abcabcabc"
"wei".repeat(5) // "weiweiweiweiwei"</code>

Array

Array.from is copied to an array and copied unchanged

<code>var arr=[1,2,3,4,5];
var ass=Array.from(arr);//[1,2,3,4,5]</code>

Array.of put into an array

Similar to new Array

<code>Array.of(1, 2, 3);//[1,2,3]</code>

fill

1 means starting from the first position, 7 means starting from the first position and followed by 7

<code>[0, 0, 0].fill(7, 1) // [0,7,7]
[0, 0, 0, 4, 6, 3, 4].fill(9, 3) // [0,0,9,9,9,9,9]</code>

Object

Object.assign shallow copy The first parameter is the target object, and the following parameters are the source object

<code>var aa = { a: 1 };  
var qq = { b: 2 };  
var zz = { c: 3 };  
Object.assign(aa, qq, zz);  
target // {a:1, b:2, c:3} 

var ss={x:1,y:2};
var bb={};
Object.assign(ss,bb);
bb.x=3;
ss//x:1,y:2;
bb//x:3,y:2;</code>

Copy directly and merge objects

<code>var ff={x:1,y:2};
var vv={k:9,l:8};
var kk=Object.assign(ff,vv)//{x:1,y:2,k:9,l:8}</code>

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