JS tamping Foundation: Javascript Perverted analysis (bottom)

function sideffecting (ary) {  ary[0] = ary[2];} function Bar (a,b,c) {    sideffecting (arguments);   return A + B + C;} Bar (1,1,1)

16, this is a big pit, especially when it comes to ES6 grammar. Knowledge Points:

• Functions/arguments

First of allThe arguments object is an Array-like object corresponding to the arguments passed to a function.

In other words arguments object , C is arguments[2], so the modification of C is the modification of arguments[2] . So the answer is 21 .

However!!!!!!

　　when a function parameter any rest parameters, any default parameters or any destructured parameters is involved, the arguments is not one mapped arguments object . Changes to C will not be reflected on the arguments, arguments is the function of the parameters.

function sideffecting (ary) {  ary[0] = ary[2];} function bar (a,b,c=3) {  ten;   sideffecting (arguments);   return A + B + C;} Bar (1,1,1)//

Let the reader understand:

[123321]

17, the problem can also be examined by the operator of the law of calculation.

This problem will make people think that is 2 > 1 && 2 < 3 actually not. This problem is equivalent to

1 2 true  true3 =  13true32  falsefalse 1 0 1 true;

So the answer is: [True,true]

3 . toString () 3 .. ToString ()3... tostring ()

18, the problem is also very funny, I did the right, the answer is:error, ‘3‘, error

Because in JS 1.1 , it 1. is a .1 valid number. So when it comes to parsing, 3.toString . does this really belong to this number or function call? It can only be a number, because it's 3. legal. We put it on the browser to see the color.

(function () {  var1;}) (); Console.log (y); Console.log (x) ;

19, the problem is relatively simple: Y is assigned to the global, X is a local variable. So the answer is: 1 and error x is not defined

var a =/123/,    =/123/== = = = B

20, the regular is the object, so even if the regular literal amount of the same, they are not equal. Answerfalse, false

var a = {}, b == = = B, object.getprototypeof (a) = = = B]

21, Knowledge points:

• Object/getprototypeof

Only Function has a prototype property, so it a.prototype is undefined .

and Object.getPrototypeOf(obj) returns a prototype of a specific object (the object's internal [[prototype]] value). Answerfalse, true

function f () {} var a = F.prototype, b == = = B

F.prototype is the object that would become the parent of any objects created with new F while object.getprototypeof return s the parent in the inheritance hierarchy.

　　F.prototype is a prototype of an F instance created using new, while Object.getprototypeof is the prototype of the F function . Please see:

A = = object.getprototypeof (new//  true//  true )

function foo () {} var oldname ="bar"; [ Oldname, Foo.name]

22, Knowledge points:

• Function/name

[‘foo‘, ‘foo‘]。the answer is because the name of the function is immutable .

[,,,].join ("")

23、知识点：[,,,] => [undefined × 3]

Because JavaScript allows the last element to be followed when the array is defined , , this is a sparse array of length three (which is three in length and not 0, 1, 23 Properties, OH). Answer:", , "

var min = math.min (), max => Max

24, Knowledge points:

• Math/min
• Math/max

Interestingly, Math.min does not pass arguments back Infinity , and Math.max does not pass arguments back -Infinity . Answer：true

var a = function.length,    new= = b

25. We know that the property of a length function instance is the number of parameters for the signature of the functions, so b.length = = 0. Another function.length is defined as 1. So not equal, the answerfalse

var a = Date (0); var New Date (0); var New  = = = b, b = = = c, a = = c]

26, about the question of date, it should be noted that

(1) If the parameter is not passed is equivalent to the current time.

(2) If it is a function call, returns a string.

Answerfalse, false, false

function foo (a) {    var  A;     return A;} function Bar (a) {    var'bye';     return A;} [Foo ('hello'), bar ('hello')]

27, in two functions, a as a parameter is actually declared, so the var a; var a = ‘bye‘ answer is actually a; a =‘bye‘。 so ["Hello", "Bye"]

JS tamping Foundation: Javascript Perverted analysis (bottom)