5 Classic JavaScript face questions

The requirements for JavaScript developers in the IT community are still high, but if JavaScript developers have the skills and experience to reach a certain level, they can easily jump to a good company, and of course the salary is not a problem. But before the interview, the interview preparation should be sufficient enough, after all, not every good developer can express themselves in a short period of time. In this article, I'll list 5 common front-end development questions. See here you prove that you must be a programmer or HR, not to read the article, to understand what the shortcomings of their own, what the problem I hope you can communicate in the message.

Issue 1: Scope

Take a look at the following code:

    (function() {    var a = b =5;    }) ();    Console.log (b);

What does the result output?

Answer:

5

The point of this question is that two different scopes, ' a ' is declared by Var as a local variable, but ' B ' is not actually defined, so it is a global variable.

This problem is also related to another important issue, that is strict mode, if you choose Strict mode, the above code will be reported uncaught Referenceerror, because B is not defined, it can help you check out some of the code problems:

    (function() {    ' use strict ';     var a = window.b =5;    }) ();    Console.log (b);

Issue 2: Create a "native" method

Write a method that repeats the string object, and enter an integer that represents the number of repeated printed words, such as:

1. Console. Log(' hello '). Repeatify(3));

This will print out the Hellohellohello. Answer:

One way to do this is to:

    String.prototype.repeatify =string.prototype.repeatify | | function (times) {    var str = '    ;  for (var i =0; i < times; i++) {    += this;    }     return str;    };

This question examines how well developers understand JavaScript inheritance and prototype attributes.

Question 3:hoisting

What is the output of the following code?

    function Test () {    console.log (a);    Console.log (foo ());     var a =1;     function foo () {    return2;    }    }    Test ();

Answer

Undefined and 2.

The above code is equivalent to the following paragraph:

    function Test () {    var  A;     function foo () {    return2;    }    Console.log (a);    Console.log (foo ());     =1;    }    Test ();

Question 4: How to perform in JavaScript

Give the results in the following code to explain your answer:

    var fullname = ' John Doe ';     var obj ={    fullname:' Colin ihrig ',    prop:{    fullname:' Aurelio De Rosa ',    Getfullname: function () {    returnthis.fullname;}}    ;    Console.log (Obj.prop.getFullname ());     var test = obj.prop.getFullname;    Console.log (Test ());

Answer:

Aurelio De Rosa and John Doe.

Question 5:call () and apply ()

After solving the previous problem let the last Console.log () output Aurelio De Rosa.

Answer:

The question is whether call () or apply (). If you don't know the difference between them, I'll build you first read what ' s the difference between Function.call and function.apply? The following line of code I use Call (), but in this case apply () will also produce the same result:

Console.log (Test.call (Obj.prop));

Original from: 5 classic JavaScript face questions

5 Classic JavaScript face questions