JavaScript handwritten code interview unbeatable 🐂01

Sorted out the front end test questions, share with everyone to study together. If you have any questions, please point out!

directory

Handwritten new function
Handwritten instanceof
Handwritten call function
Handwritten Apply function
Handwritten bind
Handwriting Debounce anti – shake function
Handwritten throttle throttling function
Hand-written array object deduplicating
Handwriting array flattening
Handwritten deep copy

1. Write new functions by hand

What new does:

An empty object is created.
Empty objectprotoPoint to the prototype of the constructorprototype.
makethisPoint to the newly created object and execute the constructor.
The result of execution has a return value and is an object. Returns the result of execution, otherwise returns the newly created object.

// Create a new constructor -- a function for new
// Constructor is a special method used to assign initial values to object member variables when an object is created
function Cat(name){
  // This refers to the window, so we need to redirect this to itself to mount the property successfully
  this.name = name
  this.say = function() {
    console.log("my name is" + this.name); }}// Write the new function
function sd_new(fn,... arg){
  const obj = {};
  // Mount the constructor prototype to the new object
  Object.setPrototypeOf(obj, fn.prototype)
  // Point this to the new object and execute the constructor
  let result = fn.apply(obj, arg);
  return result instanceof Object ? result : obj
}

/ / verification
var cat = sd_new(Cat, "shamao")
cat.say();// my name is shamao
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2. The handwritten instanceof

The advantages and disadvantages:

Advantages: Can distinguish Array, Object, and Function, suitable for judging custom class instance objects
Disadvantages: Number, Boolean, String Basic data types cannot be determined

Implementation steps:

The arguments passed in are instance L on the left, and constructor R on the right
Handles bounds, and returns false if you want to detect an object of primitive type
Take the prototype of the passed parameters, respectively
Check whether the left prototype is null, if null returns false; Return true if both archetypes are equal, otherwise continue with the left archetype.

function sd_instanceof(L,R){
    // Verify that if it is a basic data type, return false directly, because instanceof can only determine the reference type
  const baseType = ['string'.'number'.'boolean'.'undefined'.'symbol'];
  if(baseType.includes(typeof(L)) || L === null) { return false };
  
  let Lp = L.__proto__;
  let Rp = R.prototype; // The function has the prototype attribute
  
  while(true) {if(Lp === null) {return false;
      }
      if(Lp === Rp){
          return true; } Lp = Lp.__proto__; }}/ / test
const flag = sd_instanceof([], Array);
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3. Write the call function

Implementation steps:

Processing boundaries:
- Object does not exist, this refers to window;
Will “call function”Mount to theOn the FN property of the object to which this points.
Execute the fn function on “the object to which this points”, pass in the argument, and return the result.

Function.prototype.sd_call = function (context, ... args) {
    //obj does not point to window
    if(! context || context ===null) {
      context = window;
    }
    // Create a unique key value for the internal method name of the context we construct
    let fn = Symbol(a);// This refers to the function that calls call
    context[fn] = this;

    // Executing the function and returning the result is equivalent to calling itself as a method of the passed context
    returncontext[fn](... args); };/ / test
  var value = 2;
  var obj1 = {
    value: 1};function bar(name, age) {
    var myObj = {
      name: name,
      age: age,
      value: this.value,
    };
    console.log(this.value, myObj);
  }
  bar.sd_call(null); // print 2 {name: undefined, age: undefined, value: 2}
  bar.sd_call(obj1, 'tom'.'110'); {name: "top", age: "110", value: 1}
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Write the Apply function by hand

Implementation steps:

In line with the call
As distinct from the form of parameters

Function.prototype.sd_apply = function (context, args) {
    //obj does not point to window
    if(! context || context ===null) {
      context = window;
    }
    // Create a unique key value for the internal method name of the context we construct
    let fn = Symbol(a);// This refers to the function that calls call
    context[fn] = this;

    // Executing the function and returning the result is equivalent to calling itself as a method of the passed context
    returncontext[fn](... args); };/ / test
  var value = 2;
  var obj1 = {
    value: 1};function bar(name, age) {
    var myObj = {
      name: name,
      age: age,
      value: this.value,
    };
    console.log(this.value, myObj);
  }
  bar.sd_apply(null[]);// print 2 {name: undefined, age: undefined, value: 2}
  bar.sd_apply(obj1, ['tom'.'110']); {name: "top", age: "110", value: 1}
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5. Write bind

Function.prototype.sd_bind = function (context, ... args) {
    if(! context || context ===null) {
      context = window;
    }
    // Create a unique key value for the internal method name of the context we construct
    let fn = Symbol(a); context[fn] =this;
    let _this = this;
    // bind is a bit more complicated
    const result = function (. innerArgs) {
      // In the first case, if you use the new operator as a constructor after bind, instead of binding this passed in, you point this to the instantiated object
      // Since the new operator calls this to the result instance, which in turn inherits from _this, we can draw the following conclusions from our knowledge of the prototype chain
      // this.__proto__ === result.prototype //this instanceof result =>true
      // this.__proto__.__proto__ === result.prototype.__proto__ === _this.prototype; //this instanceof _this =>true
      if (this instanceof _this === true) {
        // This points to an instance of result
        this[fn] = _this;
        this[fn](... [...args, ...innerArgs]);// Es6 methods are used here to enable bind to support parameter merging
        delete this[fn];
      } else {
        It would be easy to change this to refer to the context passed in if it was just called as a normal functioncontext[fn](... [...args, ...innerArgs]);deletecontext[fn]; }};// If you bind to a constructor, you need to inherit the constructor prototype properties and methods
    // Implement inheritance by using object.create
    result.prototype = Object.create(this.prototype);
    return result;
  };
  function Person(name, age) {
    console.log(name); //' I am the name of the parameter passed in '
    console.log(age); //' I am the age passed in '
    console.log(this); // The constructor this points to the instance object
  }
  // The method to construct the prototype
  Person.prototype.say = function () {
    console.log(123);
  };

  // A normal function
  function normalFun(name, age) {
    console.log(name); //' I am the name of the parameter passed in '
    console.log(age); //' I am the age passed in '
    console.log(this); // The normal function this points to the first argument to the bind, which in our example is obj
    console.log(this.objName); //' I am the name of obj '
    console.log(this.objAge); //' I am an age from obj '
  }

  let obj = {
    objName: 'I'm the name that OBj passed in.'.objAge: 'I'm the age that OBj sent in.'};// Test as constructor call first
  // let bindFun = person.sd_bind (obj, 'I am the name of the parameter ');
  // let a = new bindFun(' I am an age');
  //   a.say(); //123

  // retest as a normal function call a;
  let bindFun = normalFun.sd_bind(obj, 'I'm the name that was passed in as a parameter');
  bindFun('I'm the age that the parameter is passed in.');
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6. Handwritten Debounce anti-shake function

Function stabilization is to execute the callback n seconds after the event is triggered. If the event is triggered again in n seconds, the timer is reset.

function debounce(fn, wait) {
    let timer = null;
    return function () {
      if(timer ! =null) {
        clearTimeout(timer);
      }
      timer = setTimeout(() = > {
        fn();
      }, wait);
    };
  }
  / / test
  function handle() {
    console.log(Math.random());
  }
  // If the window size changes, handle is triggered
  window.addEventListener('resize', debounce(handle, 1000));
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7. Handwritten throttle functions

When an event is triggered, only a certain period of time is specifiedOne callFunction. For example, send requests every once in a while while the page is scrolling

Implementation steps:

The argument passed is to execute the function fn and wait time wait.
Save the initial time now.
Returns a function that updates now to the current time if the wait time is exceeded.

function throttle(fn, wait, ... args) {
    var pre = Date.now();
    return function () {
      // The function may have input parameters
      var context = this;
      var now = Date.now();
      if (now - pre >= wait) {
        // Will execute the function this to the current scope
        fn.apply(context, args);
        pre = Date.now(); }}; }/ / test
  var name = 'mu';
  function handle(val) {
    console.log(val + this.name);
  }
  // Roll the mouse to trigger the handle
  window.addEventListener('scroll', throttle(handle, 1000.'4'));
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8. Hand-write array objects for deduplication

Keys using map cannot be duplicated, removing items with the same attributes

function uniqBy(arr, key) {
    return [...new Map(arr.map((item) = > [item[key], item])).values()];
  }
  const list = [
    { id: 1.name: 'tom' },
    { id: 1.name: 'jey' },
    { id: 2.name: 'joy'},];console.log(uniqBy(list, 'id')); // [{id:1,name:"jey"},{id:2,name:"joy"}]
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9. Handwriting array flattening

flat

let arr = [1.2[3.4], [5.6[7.8.9]]]
console.log(arr.flat(Infinity))//[1, 2, 3, 4, 5, 6, 7, 8, 9]
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join/ split

console.log(arr.toString().split(",").map(Number))//[1, 2, 3, 4, 5, 6, 7, 8, 9] 
console.log(arr.join().split(",").map(Number))//[1, 2, 3, 4, 5, 6, 7, 8, 9]
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Functional version

function flatter(arr) {
     if(! arr.length)return;
        while (arr.some((item) = > Array.isArray(item))) { arr = [].concat(... arr); }return arr;
 }
// console.log(flatter([1, 2, [1, [2, 3, [4, 5, [6]]]]]));
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10. Deep copy by hand

A deep copy of an object is essentially a recursive method of deep cloning: iterating through the object and array until it contains all the basic data types, and then copying.

Simple version of

function deepCopy(obj){
    // Check if it is a simple data type,
    if(typeof obj == "object") {// Complex data types
        var result = obj.constructor == Array ? [] : {};
        for(let i in obj){
            result[i] = typeof obj[i] == "object"? deepCopy(obj[i]) : obj[i]; }}else {
        // Assign to simple data types directly ==
        var result = obj;
    }
    return result;
}
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premium

function deepClone(obj, hash = new WeakMap(a)) {
  // If it is null or undefined, I will not copy it
  if (obj === null) return obj;

  if (obj instanceof Date) return new Date(obj);

  if (obj instanceof RegExp) return new RegExp(obj);

  // May be objects or ordinary values if functions do not need deep copies
  if (typeofobj ! = ='object') return obj;

  // Make a deep copy of an object
  if (hash.get(obj)) return hash.get(obj);

  // Find the constructor from the parent class stereotype, which points to the current class itself
  let cloneObj = new obj.constructor();

  hash.set(obj, cloneObj);

  for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
      // Implement a recursive copycloneObj[key] = deepClone(obj[key], hash); }}return cloneObj;
}

let obj = { name: 1.address: { x: 100}}; obj.o = obj;// The object has a circular reference
let d = deepClone(obj);
obj.address.x = 200;
console.log(d);
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JavaScript handwritten code interview unbeatable 🐂01

1. Write new functions by hand

2. The handwritten instanceof

3. Write the call function

Write the Apply function by hand

5. Write bind

6. Handwritten Debounce anti-shake function

7. Handwritten throttle functions

8. Hand-write array objects for deduplication

9. Handwriting array flattening

10. Deep copy by hand

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