1. Array deduplication

letArr =,2,2,3,3,4,5,6 [1]letNewArr = [... new Set (arr)] / [6] / / or Array. The from (new Set (arr))Copy the code

2. Cast String to Number

'123'* 1 / / 123'china' * 1            // NaN
null * 1            // 0
undefined * 1    // NaN

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+ '666'/ / 666 +' '                    // 0
+ null              // 0
+ 'china'               // NaN
+ undefined    // NaN

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When + is interpreted as a join operator rather than an addition operator, two ~~ substitutions can be used. For integers ~~ yields the same result as math.floor () (a tilde ~, called the “bitwise inverse operator”, is equivalent to -n-1. So ~15 = -16.)

3, includes

letArr = [1,2,3,4,5] console.log(arr.includes(1) == Arr.indexof (1)! / / = 1)true
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Determine whether an element exists in a string or array using includes instead of indexOf

4, URLSearchParams

Basic usage

 let url = new URLSearchParams(location.search.slice(1));
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Using URL construction

 let location = 'http://www.baidu.com?id=2'
 let _url = (new URL(location)).searchParams;
 console.log(_url.get("id"/ / 2))Copy the code

Gets/sets parameters

  • Get (key) : obtains parameters
  • Set (key) : sets parameters
  • Append (key, value) :

5. Objects are de-merged

Object.assign

var obj1 = { a : 1 };

var obj2 = { b : 2 };

var obj3 = { c : 3 };

console.log(Object.assign(obj1, obj2, obj3))//{ a : 1, b : 2, c:3 }
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Extended operator

let obj1 = { a : 1, b : 2 };
let obj2 = { a : 2, c : 3, d : 4 };
letnewObj = { ... obj1,... obj2 }; console.log(newObj) //{a: 2, b: 2, c: 3, d: 4}Copy the code

Tiling multidimensional arrays

var arr1 = [1, 2, [3, 4]]; arr1.flat(); // [1, 2, 3, 4] var arr2 = [1, 2, [3, 4, [5, 6]]]; arr2.flat(); // [1, 2, 3, 4, [5, 6]] var arr3 = [1, 2, [3, 4, [5, 6]]]; arr3.flat(2); // [1, 2, 3, 4, 5, 6] // Use Infinity as the depth to expand the nested array arr3. Flat (Infinity); // [1, 2, 3, 4, 5, 6]Copy the code

The flat() method removes empty items from the array:

var arr4 = [1, 2, , 4, 5];
arr4.flat();
// [1, 2, 4, 5]
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Boolean Filters all false values in the array

let arr = [ 1 , null , false , 2 , 3 , NaN , ' '] the console. The log (a.f ilter (Boolean)) / / [1, 2, 3]Copy the code

8, integer

For a digital | 0 can be integer, negative number also applies, num | 0

1.3 | 0 // 1
-1.9 | 0 // -1
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9, | | and use &&

/ / scenario 1function b(a) {
  if (a) {
    return a
  } else {
    return ' '} // Scenario 2function b(a) {
  return a || ' '
}
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The use of the above is | |, also called short circuit processing. This is common in if conditions, but can also be used directly in statements. If the first argument is true, the value of the first argument is taken; if the first argument is not true, the value of the second argument is taken. && coincided with | | instead. If the first argument is true, it takes the value of the second argument. It is common to use && instead of if-else, for example:

if(a >=5){   alert("Hello"); 
} 
//a >= 5 && alert("Hello"); 
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Use objects instead of switch/if

Public content:let a = 'VIP'Scenario 1if (a === 'VIP') {
  return1}else if (a === 'SVIP') {
  return2} Scenario 2 Switch (a) {case 'VIP'
    return 1
    break
  case 'SVIP'
    return 2
    break} scenario 3let obj = {
  VIP: 1,
  SVIP: 2
}
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Available this method maps the state meaning in Chinese, for example, pay state usually get is 1, 2 and 4 of this value, but the list requires display the corresponding Chinese state Did not pay | | in the payment has been refund, etc

Filter object properties with destructively assigned values

Const {inner, outer,... restProps } = { inner:'This is inner',
  outer: 'This is outer',
  v1: '1',
  v2: '2',
  v4: '3'
};
console.log(restProps);
// {v1: "1", v2: "2", v4: "3"}
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12. Digital amount is formatted in thousands of digits

let num = 123455678;
letNum1 = 123455678.12345;let formatNum = num.toLocaleString('en-US');
let formatNum1 = num1.toLocaleString('en-US'); console.log(formatNum); / / 123455678 console log (formatNum1); / / 123455678123Copy the code