JS is very clever

Generates random combinations of letters and arrays

Math.random().toString(36).substr(2);
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Formatting time

const dateFormatter = (formatter, date) = > {
	date = (date ? new Date(date) : new Date)
	const Y = date.getFullYear() + ' ',
          M = date.getMonth() + 1,
          D = date.getDate(),
          H = date.getHours(),
          m = date.getMinutes(),
          s = date.getSeconds()
    return formatter.replace(/YYYY|yyyy/g, Y)
        			.replace(/YY|yy/g, Y.substr(2.2))
        			.replace(/MM/g, (M < 10 ? '0' : ' ') + M)
        			.replace(/DD/g, (D < 10 ? '0' : ' ') + D)
        			.replace(/HH|hh/g, (H < 10 ? '0' : ' ') + H)
        			.replace(/mm/g, (m < 10 ? '0' : ' ') + m)
        			.replace(/ss/g, (s < 10 ? '0' : ' ') + s)
}

dateFormatter('YYYY/MM/DD hh:mm:ss'.new Date()) / / 2021/06/21 11:11:17
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Gets the actual type of the variable

const trueTypeOf = (obj) = > {
  return Object.prototype.toString.call(obj).slice(8, -1).toLowerCase();
};

console.log(trueTypeOf(' '));
// string
console.log(trueTypeOf(0));
// number
console.log(trueTypeOf());
// undefined
console.log(trueTypeOf(null));
// null
console.log(trueTypeOf({}));
// object
console.log(trueTypeOf([]));
// array
console.log(trueTypeOf(0));
// number
console.log(trueTypeOf(() = > {}));
// function
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1. If multiple conditions judge

/ / redundancy
if (x === 'abc' || x === 'def' || x === 'ghi' || x ==='jkl') {}

/ / concise
if (['abc'.'def'.'ghi'.'jkl'].includes(x)) {}
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2. if… else…

/ / redundancy
let test: boolean;
if (x > 100) {
    test = true;
} else {
    test = false;
}

/ / concise
let test = x > 10;
let text = x > 10 ? true : false
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• Multiple conditions determine the same execution method

if(status === 0 || status === 1 || status === 2 || status === 3) {
    console.log('Button can be clicked');
}
/ / = >

if([0.1.2.3].includes(status)) {
    console.log('Button can be clicked');
}
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• There are multiple possibilities for different situations

// status Is not a value or the value is too large
const statusTextObject = {
    100: 'Deleted'.101: 'not started'.102: 'In class'.103: 'Class dismissed'.104: 'Assessed'
}
text = statusTextObject[status] || The '-';

// Replace the key of the object with the value of status.
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3. Check for Null, Undefined, and Null values

/ / redundancy
if(first ! = =null|| first ! = =undefined|| first ! = =' ') {
    let second = first;
}

/ / concise
let second = first || ' ';
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4. Function conditional call

/ / redundancy
function test1() {
  console.log('test1');
};
function test2() {
  console.log('test2');
};
var test3 = 1;
if (test3 == 1) {
  test1();
} else {
  test2();
}

/ / simple
(test3 === 1? test1:test2)();
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5. Switch multiple conditions

/ / redundancy
switch (data) {
  case 1:
    test1();
  break;

  case 2:
    test2();
  break;

  case 3:
    test();
  break;
  // so on...
}

/ / concise
var data = {
  1: test1,
  2: test2,
  3: test
};

data[anything] && data[anything]();
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6. Implicit return

/ / redundancy
function getArea(diameter) {
  return Math.PI * diameter
}

/ / concise
getArea = diameter= > (
  Math.PI * diameter;
)
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7. Plain array de-duplication & object array de-duplication

const uniqueArr = (arr) = > [...new Set(arr)];

console.log(uniqueArr([1.2.3.1.2.3.4.5]));
// [1, 2, 3, 4, 5]


const uniqueElementsBy = (arr, fn) = >arr
.reduce((acc, v) = > {if(! acc.some(x= > fn(v, x))) acc.push(v);return acc;}, []);
 
uniqueElementsBy([{id: 1.name: 'Jhon'}, {id: 2.name: 'sss'}, 
{id: 1.name: 'Jhon'}].(a, b) = > a.id == b.id)
// [{id: 1, name: 'Jhon'}, {id: 2, name: 'sss'}]

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8. Fetch the value of the corresponding property from the array

const reducedFilter = (data, keys, fn) = >data.filter(fn)
.map(el= >keys.reduce((acc, key) = > {acc[key] =el[key];returnacc; }, {}));const data = [
  {
    id: 1.name: 'john'.age: 24
  },
  {
    id: 2.name: 'mike'.age: 50}];let a = reducedFilter(data, ['id'.'name'].item= > item.age > 24); // [{ id: 2, name: 'mike'}]
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9. Return cur.push(v*2),cur

Let arr = [1, 2, 3, 4] const b = arr. Reduce ((cur, v) = > [... cur, v * 2], []) const b1 = arr. Reduce ((cur, v) = > {/ / return directly Cur.push (v*2) returns an error because push does not return an array, Return cur.push(v*2),cur},[]) const b2=arr. Reduce ((res, cur)=> {res.push(cur *2); return res; }, []) / /,4,6,8 [2]Copy the code

• return cur.push(v*2),curIs equivalent toreturn cur