JS Pen questions (not updated regularly)

1 finding the largest element in a numeric array (using the Math.max function)

Math.max.apply (this, arr)

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2 Convert a numeric array into a function array (each function pops up the corresponding number)

 for (var i=0;i<arr.length;i++) {    var tmp=Arr[i];    Arr[i]=function(TMP) {        returnfunction() {            alert (TMP);        }    } (TMP)} or Arr.map (function(e) {    returnfunction() {alert (e)};});

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3 Sort an object array (sorting criteria is the number of attributes per element object)

Objarray.sort (A, b){    return Object.keys (a). length-Object.keys. length;});

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4 Print out Fibonacci using JavaScript (without global variables)

function Fibonacci (n) {    if(n==0| | N==1) {        return  n;    }     return Fibonacci (n-1) +fibonacci (N-2);} Fibonacci (5);

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5 implements the following syntax functions: var a = (5). Plus (3). Minus (6); 2

number.prototype.plus=function(n) {    returnthis +N;} Number.prototype.minus=function(n) {    returnthis-N;}

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6 implements the following syntax functions: var a = Add (2) (3) (4); 9

// determines whether a function or a value is returned function Add (n) {    var f=function(m) {        return Add (n+m);    };    f.tostring=f.valueof=function() {        return  n;    };     return F;}

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7 Variable Promotion

if inch window)) {    var a = 1;} alert (a);

// [alert:undefined]

View Answer 8 Variable objects

var a = 1,    function  A (x) {        && A (--x);    }; alert (a);

// [Alert:1] // precedence: Function parameters > Function declarations > variable declarations // equivalent to function expression   b = function (x) {//        x && B (--x); //     };

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function A (x) {    return x * 2;} var A;alert (a);

// alert:function A (x) {//     return x * 2; //  }

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9 Arguments objects

function b (x, Y, a) {    arguments[2] = ten;    alert (a);} B (1, 2, 3); function b (x, Y, a) {    arguments[2] = ten;    alert (a);} B (1, 2);

// Alert:10 and alert:undefined // The value of the properties-indexes is shared with the arguments actually passed in.  //  This share is not really a shared memory address, but 2 different memory addresses, using the JavaScript engine to ensure that 2 values are always the same, of course, if the index value is less than the number of parameters passed in. 

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Ten this

function A () {    alert (this);} A.call (null);

// alert: [Object Window] // The call method takes the global object as the value of this if the first parameter passed in to the object caller is null or undefined. 

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44-Channel JS Puzzle

JS Pen questions (not updated regularly)