1. Locate the array element
function indexOf(arr, item) {
return arr.indexOf(item);
}
Copy the code2. Array summing
function sum(arr) {
let res = 0;
for(let i = 0; i < arr.length; i ++){
res += arr[i];
}
return res;
}
Copy the codeforEach
function sum(arr) {
let res = 0;
arr.forEach((value, index, array) = > {
res += value;
})
return res;
}
Copy the codereduce
function sum(arr) {
return arr.reduce((pre,cur) = >{
returnpre + cur; })}Copy the code3. Remove an element from an array to return a new array
filter
function remove(arr, item) {
return arr.filter((res) = > {
return res != item;
})
}
Copy the codefor+push
function remove(arr, item) {
let res = [];
arr.forEach((value, index) = > {
if(value != item) {
res.push(value);
}
})
return res;
}
Copy the code4. Remove elements from the array to modify the original array
splice
function removeWithoutCopy(arr, item) {
for(let i = 0; i < arr.length; i ++) {
if(arr[i] === item){
arr.splice(i,1); i --; }}return arr;
}
Copy the codeIf I subtract one element from the array, I —
5. Add elements to return a new array
concat
function append(arr, item) {
return arr.concat(item);
}
Copy the code. extension
function append(arr, item) {
return [...arr, item];
}
Copy the codeFor \ slice shallow copy + push
6 Deletes the last element of the array
Returns a new array
function truncate(arr) {
let newarr = arr.slice(0)
newarr.pop()
return newarr
}
Copy the code7 Adding Elements
function prepend(arr, item) {
let newarr = arr.slice(0);
newarr.unshift(item);
return newarr;
}
Copy the code8 Delete the first element of the array
function curtail(arr) {
let newarr = arr.slice(0);
newarr.shift();
return newarr;
}
Copy the code9 Array Merging
function concat(arr1, arr2) {
let newarr = arr1.concat(arr2);
return newarr;
}
Copy the codefunction concat(arr1, arr2) {
let newarr = [...arr1, ...arr2];
return newarr;
}
Copy the code10 Add elements (add at the specified location)
function insert(arr, item, index) {
let newarr = arr.slice(0);
newarr.splice(index, 0, item);
return newarr;
}
Copy the code11 counts
function count(arr, item) {
let num = 0;
arr.forEach(val= > {
if(val === item) num ++;
})
return num;
}
Copy the code12 Find duplicate elements
function duplicates(arr) {
let res = [];
arr.forEach( v= > {
if(arr.indexOf(v) ! == arr.lastIndexOf(v) && res.indexOf(v) === -1){ res.push(v); }})return res;
}
Copy the code13 to the second power
function square(arr) {
let res = arr.map((value, index, array) = > {
return value * value;
});
return res;
}
Copy the code14 Locate elements
function findAllOccurrences(arr, target) {
let res = [];
arr.forEach((value, index) = > {
if(value === target) { res.push(index); }});return res;
}
Copy the code15 Avoid global variables
function globals() {
/ / plus the let
let myObject = {
name : 'Jory'
};
return myObject;
}
Copy the code16 Correct function definition
function functions(flag) {
if (flag) {
var getValue = function() { return 'a'; }}else {
var getValue = function() { return 'b'; }}return getValue();
}
Copy the code17 Use parseInt correctly
function parse2Int(num) {
return parseInt(num, 10);
}
Copy the code18 Be exactly equal
function identity(val1, val2) {
return val1 === val2;
}
Copy the code19 the timer
function count(start, end) {
console.log(start++);
var timer = setInterval(
function(){
if(start <= end) {
console.log(start++);
}else{
clearInterval(timer); }},100);
return {
cancel: function(){
clearInterval(timer); }}}Copy the code20 Process Control
function fizzBuzz(num) {
if(num % 3= = =0 && num % 5= = =0) {
return 'fizzbuzz';
}else if(num % 3= = =0) {
return 'fizz';
}else if(num % 5= = =0) {
return 'buzz';
}else if(num === null || typeofnum ! = ='number') {return false;
}else{
returnnum; }}Copy the code21 Function parameters are passed
function argsAsArray(fn, arr) {
return fn.apply(this, arr);
}
Copy the codeFunction context
//apply
function speak(fn, obj) {
return fn.apply(obj);
}
//call
function speak(fn, obj) {
return fn.call(obj);
}
//bind
function speak(fn, obj) {
return fn.bind(obj)();
}
Copy the code23 Return function
function functionFunction(str) {
return f = function(str2) {
return str + ', '+ str2; }}Copy the code24 Use closures
function makeClosures(arr, fn) {
let result = [];
ForEach and let can be circumvented
arr.forEach((index,value) = > {
result.push(() = > {
returnfn(index); })})return result;
}
Copy the codeExecute function immediately
function makeClosures(arr, fn) {
var result = [];
ForEach and let can be circumvented
for(var i = 0; i < arr.length; i ++) {
(function (i) {
result[i] = function() {
return fn(arr[i])
}
})(i);
}
return result;
}
Copy the code25 Quadratic encapsulation function
function partial(fn, str1, str2) {
return function(str3) {
returnfn(str1, str2, str3); }}Copy the code26 USES the arguments
function useArguments() {
let arr = Array.prototype.slice.call(arguments); // Convert to an array
let res = 0;
arr.forEach((value) = > {
res += value;
})
return res;
}
Copy the code27 Use apply to call the function
function callIt(fn) {
return fn.apply(this, [].slice.call(arguments.1))}Copy the code28 Quadratic encapsulation function
function partialUsingArguments(fn) {
let args = [].slice.call(arguments.1);
return reslut = function() {
return fn.apply(this, args.concat([].slice.call(arguments))); }}Copy the code29 It is difficult to make currie
function curryIt(fn) {
let args = [];
let result = function(arg) {
args.push(arg);
if(args.length < fn.length) {
return result;
}else{
return fn.apply(this, args); }}return result;
}
Copy the code30 or operation
function or(a, b) {
return (a || b);
}
Copy the code31 and operation
function and(a, b) {
return (a && b);
}
Copy the code32 module
function createModule(str1, str2) {
let obj = {
greeting: str1,
name: str2,
sayIt: function(){
return obj.greeting + ', '+ obj.name; }}return obj;
}
Copy the code33 Binary Conversion
function valueAtBit(num, bit) {
let res = num.toString(2);
return res[res.length - bit];
}
Copy the code34 Binary Conversion
function base10(str) {
return parseInt(str, 2);
}
Copy the code35 Binary Conversion
function convertToBinary(num) {
let res = num.toString(2);
while(res.length < 8) {
res = '0' + res;
}
return res;
}
Copy the code36 multiplication
function multiply(a, b) {
let str1 = a.toString();
let str2 = b.toString();
let lenA = (str1.indexOf('. ') = = = -1)?0: (str1.length - 1 - str1.indexOf('. '))
let lenB = (str2.indexOf('. ') = = = -1)?0: (str2.length - 1 - str2.indexOf('. '))
let len = Math.max(lenA, lenB);
let result = parseFloat(a * b).toFixed(len);
return result;
}
Copy the code37 Changing context
function alterContext(fn, obj) {
return fn.apply(obj);
}
Copy the code38 Change object attributes in batches
function alterObjects(constructor, greeting) {
constructor.prototype.greeting = greeting;
}
Copy the code39 Attribute traversal
function iterate(obj) {
let result = [];
for(let key in obj){
if(obj.hasOwnProperty(key)){
result.push(key+":"+obj[key]); }}return result;
}
Copy the code40 Check whether digits are included
function containsNumber(str) {
return /\d./.test(str);
}
Copy the code41 Check for duplicate strings
function containsRepeatingLetter(str) {
return /([a-zA-Z])\1/.test(str);
}
Copy the code42 Check whether the letter ends with a vowel
function endsWithVowel(str) {
return /[a,e,i,o,u]$/i.test(str);
}
Copy the code43 Obtain the specified string
function captureThreeNumbers(str) {
let arr = str.match(/\d{3}/);
if(arr){
return arr[0];
}else{
return false; }}Copy the code44 Check whether the format is correct
function matchesPattern(str) {
return /^\d{3}-\d{3}-\d{4}$/.test(str);
}
Copy the code45 Check whether it conforms to the USD format
function isUSD(str) {
return / ^ $\ \ d {1, 3} (\ d {3}) * (. \ \ d {2})? $/.test(str);
}
Copy the code