JavaScript 44 Puzzlers
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/*44 javascript puzzlers
http://javascript-puzzlers.herokuapp.com/
// 001
var res = ['1','2','3'].map(parseInt);
console.log(res);// 输出结果为：[1,NaN,NaN]
// 输出结果为：[parseInt('1',0),parseInt('2',1),parseInt('3',2)]
function foo1(){ // 查看传入的参数都是啥；
var l = arguments.length;
console.log('arguments begin:');
for(var i=0;i<l;i++){
console.log(arguments[i]);
}
console.log('arguments end;');
}
var res2 = ['1','2','3'].map(foo1);
// map方法会给原数组中的每一个元素都按顺序调用一次callback函数；
// callback函数会被传入3个参数：数组元素，元素索引，原数组本身；
var a = 'global a';
function foo2(){
console.log(this.a);
}
foo2(); // 直接调用会输出 'global a'
var obj = {};
obj.a = 'object a';
var res = [1,2,3].map(foo2,obj); // 会输出三个'object a'
// map方法传入一个回调函数，并且传入一个回调函数中的this对象；
console.log(res); // [undefined, undefined, undefined]
// 002
var res = [typeof null, null instanceof Object];
console.log(res); // ['object',false]
// js共有6种数据类型 Undefined,String,Number,Boolean,Object,Null
// 每种对应的typeof为'undefined','string','number','boolean','object','object'
// Function 不是数据类型，但是typeof Function 返回 'function'
// JavaScript instanceof运算符代码
// http://www.ibm.com/developerworks/cn/web/1306_jiangjj_jsinstanceof/
function instance_of(L,R){ // L表示左表达式，R表示右表达式
var O = R.prototype; // 取R的显示原型
L = L.__proto__; // 取L的隐式原型
while(true){
if(L === null){
return false;
}
if(O === L){ // 这里重点：当O严格等于L时，返回true
return true;
}
L = L.__proto__;
}
}
function Aoo(){}
function Foo(){}
Foo.prototype = new Aoo(); // JavaScript原型继承
var foo = new Foo();
console.log(foo instanceof Foo); // true
console.log(foo instanceof Aoo); // true
console.log(Object instanceof Object); //true
console.log(Function instanceof Function); //true
console.log(Number instanceof Number); // false
console.log(String instanceof String); // false
console.log(Function instanceof Object); // true
console.log(Foo instanceof Function); // true
console.log(Foo instanceof Foo); // false
// 003
//var res = [[3,2,1].reduce(Math.pow),[].reduce(Math.pow)]; // 这一行就会直接报 TypeError，不能对空数组调用reduce方法；
//console.log(res);
//var res = [3,2,1].reduce(Math.pow);
//console.log(res); // 输出9 , Math.pow(3,2),Math.pow(9,1)
function foo1(){
var l = arguments.length;
console.log('arguments begin:');
for(var i=0;i<l;i++){
console.log(arguments[i]);
}
console.log('arguments end:');
}
//var res = ['a','b','c'].reduce(foo1);
// reduce中的回调函数会获得四个参数: 初始值（或者上一次回调函数的返回值，没有返回值就是undefined），当前值，当前值索引，原数组
// 如果没有初始值，就会把数组第一个值作为初始值；
//var res = ['a','b','c'].reduce(foo1,'A');
//var obj = {};
//var res = [1,2,3].reduce(obj); // 如果回调函数不是函数，也会直接抛出TypeError异常
// 004
var val = 'smtg';
console.log('Value is ' + (val==='smtg')?'Something':'Nothing');
// + 优先级 大于 ? , 等价于 'Value is true'?'Something':'Nothing'
// 005
var name='World';
(function(){
if(typeof name === 'undefined'){
var name = 'Jack';
console.log('Goodbye '+name);
}else{
console.log('Hello '+name);
}
})();
(function(){
var a;
if(typeof a === 'undefined'){
var name = 'Jack';
console.log('Goodbye '+name);
}else{
console.log('Hello '+name);
}
})();
(function(){
var a='';
if(typeof a === 'undefined'){
var name = 'Jack';
console.log('Goodbye '+name);
}else{
console.log('Hello '+name); // 这个变量的确被提升了；Hoisting
}
})();
(function(){
var a='';
if(typeof a === 'undefined'){
var name = 'Jack';
console.log('Goodbye '+name);
}else{
console.log('Hello '+name1); // 这个就会报异常，name1 is not defined
}
})();
// 006
var END = Math.pow(2,53); // 9007199254740992
var START = END - 100;
var count = 0;
//for(var i= START;i>> 0;
if (typeof fun !== 'function') {
throw new TypeError();
}
var res = [];
var thisArg = arguments.length >= 2 ? arguments[1] : void 0;
for (var i = 0; i < len; i++) {
if (i in t) { // 首先判断是否在数组内；
var val = t[i];
// NOTE: Technically this should Object.defineProperty at
// the next index, as push can be affected by
// properties on Object.prototype and Array.prototype.
// But that method's new, and collisions should be
// rare, so use the more-compatible alternative.
if (fun.call(thisArg, val, i, t)) {
res.push(val);
}
}
}
return res;
};
}
// 008
var one = 0.1;
var two = 0.2;
var six = 0.6;
var eight = 0.8;
var res = [two-one==one, eight-six==two];
console.log(res); // [true,false]
var arr = [0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9];
for(var i=0;i<9;i++){
for(var j=0;j4? console.log(arr[i]+'+'+arr[j]+'='+(arr[i]+arr[j])):0;
(arr[i]-arr[j]+'').length>4? console.log(arr[i]+'-'+arr[j]+'='+(arr[i]-arr[j])):0;
}
}
// JavaScript中计算精度丢失的问题 IEEE754 http://rockyee.iteye.com/blog/891538
// 0.00011001100110011001100110011001100110011001100110011001
//+ 0.00110011001100110011001100110011001100110011001100110011
// = 0.01001100110011001100110011001100110011001100110011001100
// 转换成10进制之后得到:0.30000000000000004
// 009
function showCase(value){
switch(value){
case 'A':
console.log('Case A');
break;
case 'B':
console.log('Case B');
break;
case undefined:
console.log('undefined');
break;
default:
console.log('Do not know');
}
}
showCase(new String('A'));
showCase('B');
// switch是严格比较， String实例和字符串是不一样的；
console.log(typeof 'A');
console.log(typeof new String('A'));
console.log('A' === new String('A'));
// 010
function showCase2(value){
switch(value){
case 'A':
console.log('Case A');
break;
case 'B':
console.log('Case B');
break;
case undefined:
console.log('undefined');
break;
default:
console.log('Do not know!');
}
}
showCase2(String('A'));
// String(x) 并不创建对象；
console.log(typeof 'A');
console.log(typeof String('A'));
console.log('A' === String('A'));
// 011
function isOdd(num){
return num%2 == 1;
}
function isEven(num){
return num%2 == 0;
}
function isSane(num){
return isEven(num)||isOdd(num);
}
var values = [7,4,'13',-9,Infinity];
var res = values.map(isSane);
console.log(values);
console.log(res);
// 012
var res1 = parseInt(3,8);
var res2 = parseInt(3,2);
var res3 = parseInt(3,0);
console.log(res1);
console.log(res2);
console.log(res3);
// 013
var res = Array.isArray(Array.prototype);
console.log(res);
// Array.prototype => []
// 014
var a=[0];
if([0]){
console.log(a==true);
}else{
console.log('wut');
}
console.log(a==true); // false
console.log(a==false); // true
var b=[0,1];
console.log(b==true); // false
console.log(b==false); // false
if(b){
console.log('b is true');
}else{
console.log('b is false');
}
// JavaScript-Equality-Table
var obj = {}; // 图片上面有表示
if(obj){
console.log('obj if true');
}else{
console.log('obj if false');
}
if(a===b){ // undefined === undefined
var a = 'a';
var b = 'b';
console.log('a===b');
}else{
console.log('a!=b');
}
// JavaScript-Equality-Table 记忆：括号不恒等，非数(NaN)空象({})恒不等；
// 015
var res = ([] == []);
console.log(res);
// 见上图
// 016
var res1 = '5'+3;
var res2 = '5'-3;
console.log(res1);
console.log(res2);
console.log(typeof res1);
console.log(typeof res2);
var res3 ='5'-'3';
console.log(res3);
console.log(typeof res3); // 减号尽可能把操作数变为数字；
var res4 = 'a' - '1'; // 就连NaN 的typeof也是数字
console.log(res4); // NaN
console.log(typeof res4); // number
// 017
var res = 1+-+++-+1; // 系统提示错误，Uncaught ReferenceError:
console.log(res);
+1; // ok
-+1; // OK
+-+1; // OK
++-+1; // Uncaught ReferenceError;
1+-+-+1; // 2 OK
++1;// Uncaught ReferenceError
var i=1;
++i;// 2
++-+i ; // Uncaught ReferenceError
// 018
var ary = Array(3);
ary[0] = 2;
var res = ary.map(function(elm){return '1';});
console.log(res); // ["1"]，length = 3
var res2 = ary.map(function(elm){return elm;});
console.log(res2); // 好像是清除了空的元素 ,length = 3
console.log(ary); // 但是这个也是 [2]没有空元素,length = 3
var ary2 = [];
ary2[0] = 0,ary2[10] = 10;
var res3 = ary2.map(function(elm) {return elm;});
console.log(res3);
console.log(ary2);
console.log(res3[10]); // 还是一样的稀疏矩阵
// Array.prototype.map 的 polyfill.
Array.prototype.map = function(callback, thisArg) {
var T, A, k;
if (this == null) {
throw new TypeError(' this is null or not defined');
}
var O = Object(this);
var len = O.length >>> 0;
if (typeof callback !== 'function') {
throw new TypeError(callback + ' is not a function');
}
if (arguments.length > 1) {
T = thisArg;
}
A = new Array(len);
k = 0;
while (k < len) {
var kValue, mappedValue;
if (k in O) {
kValue = O[k];
mappedValue = callback.call(T, kValue, k, O);
A[k] = mappedValue;
}
k++;
}
return A;
};*/
$(function() {
init();
});// js44function init(e) {}/*
*
*
* // 019
function sidEffecting(ary) {
ary[0] = ary[2];
}
function bar(a,b,c) {
c = 10;
console.log(arguments);
console.log(a,b,c);
sidEffecting(arguments);
console.log(arguments);
console.log(a,b,c);
return a+b+c;
}
//var res = bar(1,1,1);
//console.log(res); // 21
function bar2(a, b, c=3) { // 如果有默认值，就无法用arguments方式修改了；
c = 10;
console.log(arguments); // [1,1,1]
console.log(a,b,c);
sidEffecting(arguments);
console.log(arguments); // [1,1,1]
console.log(a,b,c);
return a+b+c;
}
//var res2 = bar2(1,1,1);
//console.log(res2); // 12
//var res3 = bar2(1,1);
//console.log(res32); // 12
function bar3(a,b,c) { // 如果传入的参数不够，也无法用arguments方式修改；
console.log(typeof c);
console.log(typeof arguments[2]);
c = 10;
console.log(typeof c);
console.log(arguments);
console.log(a,b,c);
sidEffecting(arguments);
console.log(arguments);
console.log(a,b,c);
return a+b+c;
}
var res4 = bar3(1,1);
console.log(res4);
// 020
var a = 111111111111111110000, b = 1111;
//123456789012345678901
var c = a+ b;
var a1 = 2147483647;
var a2 = Math.pow(2,53); // 可以表示的最大的数字？第6题 9007199254740992(共16位)
console.log(c); // 111111111111111110000 与数值的存储方式有关
console.log(typeof a); // number
console.log(a1+b);
console.log(a2);
console.log(a2+1); // a2+1已经不变了；但是a2+2还是会变的；
var a3 = 12345678901234567;
console.log(a3); // 12345678901234568
console.log(a3+1);
// 021
//var x = [].reverse;
//x(); // Uncaught TypeError: Array.prototype.reverse called on null or undefined
var arr = ["a","b","c"];
//console.log(arr.reverse());
var x = arr.reverse;
var res = x.call(arr);
console.log(res);
var arr1 = ["d","e","f"];
var res2 = x.call(arr1);
console.log(res2);
// 022
var res = Number.MIN_VALUE >0;
console.log(res); // true
console.log(Number.MIN_VALUE); // 5e-324，接近0，但不是负数；
console.log(Number.MAX_VALUE); // 1.7976931348623157e+308
// 023
var res = [1<2<3,3<2<1];
console.log(res); // [true,true]
var res1 = [true<3,falsec;
var res4 = a<c;
console.log(res1,res2,res3,res4);
console.log(a.toString());
console.log(a.valueOf());
console.log(a.valueOf()-b.valueOf());
console.log(!!(a.valueOf()-b.valueOf()));
// 029
var a = {}, b = Object.prototype;
var res = [a.prototype === b,Object.getPrototypeOf(a)===b];
console.log(res);
console.log(a.__proto__ === b); // true
console.log(a.prototype); // undefined
console.log(Object.getPrototypeOf(1) === Number.prototype); // true
//console.log(1.__proto__); // 这样写会出错
// Object.getPrototypeOf(obj) 返回一个具体对象的原型
// 030
function f() {}
var a = f.prototype, b = Object.getPrototypeOf(f);
var res = (a===b);
console.log(res);
console.log(b===Function.prototype); // b is f.__proto__
var a1 = new f();
console.log(a1.__proto__ === a);
// 031
function foo() {}
var oldName = foo.name;
foo.name = "bar";
console.log(oldName, foo.name); // 函数的name不能修改
var foo2 = function (e) {}
console.log(foo2.name); // 匿名函数的name就是一个空字符串
console.log(foo2.name === "");
foo2.name = "bar2";
console.log(foo2.name); // 匿名函数的name也不能修改
// 032
var res = "1 2 3".replace(/\d/g, parseInt);
console.log(res);
function showArgs() {
console.group('show Args');
var len = arguments.length;
for(var i=0;i<len;i++){
console.log(arguments[i]);
}
console.groupEnd();
}
function showArgs2(e) {
console.log(arguments);
}
//"1 2 3".replace(/\d/g,showArgs);
// 如果replaceText为函数，对于每一个匹配的子字符串，调用该函数时带有m+3个参数，此处m是regExp中捕获的
// 左括弧的个数。第一个参数是匹配的子字符串，接下来的m个参数是查找中捕获的全部结果。第m+2个参数是在stringObj
// 中匹配出现的偏移量，而第m+3个参数为stringObj
//"1a2b3c4".replace(/(\d+)(\D+)(\d+)/g,showArgs); // 查看匹配的m个参数
// 替换模式中的子表达式
var res = "1a2b3c4d".replace(/(\d+)(\D+)/g,"$2$1"); // 数字和字母替换
console.log(res);
"1a2b3c4d".replace(/(\d+)(\D+)/g,showArgs2); // 看看匹配的结果
//"1a2b3c4d".replace(/(\d+)(\D+)/g,function($0,$1,$2){
// console.group('show $');
// console.log($0); // 匹配到的字符串
// console.log($1);
// console.log($2);
// console.groupEnd();
//});
var res = "123a456".replace(/\D+/g,"{$&}"); // 给匹配的内容加上{}
//console.log(res);
//var res = "123a456".replace(/\D+/g,"$`"); // 匹配字符串左边的字符
//var res = "123a456".replace(/\D+/g,"$'"); // 匹配字符串右边的字符
//console.log(res);
// 033
function f() {}
var parent = Object.getPrototypeOf(f);
//console.log(f.name);
//console.log(parent.name);
//console.log(typeof eval（f.name));
//console.log(typeof eval（parent.name));
// eval（) 函数可计算某个字符串，并执行其中的JavaScript代码；
function a(e) {
console.log("this is a function");
}
eval（"a"); // 就是一个函数
a;
var b = function(){}; // 匿名函数，其name是空字符串；
eval（"b");
var res = eval（"");
console.log(res);
// 034
var lowerCaseOnly = /^[a-z]+$/;
var res = [lowerCaseOnly.test(null),lowerCaseOnly.test()];
console.log(res);
// test方法，返回一个boolean值，它指出在被查找的字符串中是否存在模式;
var reg = /\D/g;
console.log(reg.lastIndex);
console.log(reg.test("123abc89"),reg.lastIndex);
console.log(reg.test("123abc89"));
console.log(reg.test("123abc89"));
console.log(reg.test("123abc89"),reg.lastIndex); // 如果是全局正则，注意lastIndex熟悉
// 035
var res = [,,,].join(",");
console.log(res);
//var arr = [,,,];
//console.log(arr); // []
//console.log(arr.length); // 3
//console.log(arr[0]); // undefined
//console.log(arr.join("*")); // **
var arr2 = [undefined,undefined,undefined,];
console.log(arr2);
console.log(arr2.length);
console.log(arr2[0]);
console.log(arr2.join("*")); // **
// 036
var a = {class:"Animal",name:'Fido','if':"iiff"};
console.log(a.class); // class是关键字
console.log(a['class']); // 推荐使用
console.log(a.if);
console.log(a['if']);
// 037
var a = new Date("epoch");
console.log(a); // Invalid Date
console.log(typeof a); // object
console.log(a instanceof Date); // true; a 是Date
// 038
var a = Function.length, b = new Function().length;
console.log(a===b);
console.log(Function.length); // 这个就是1
console.log(new Function("x","y","return x+y").length); // 这个表示函数的参数个数
var b = new Function("x","y","return x+y");
console.log(b(2,2));
// 039
var a = Date(0);
var b = new Date(0);
var c = new Date();
console.log([a===b, b===c, a===c]);
//console.log(a);
//console.log(b);
//console.log(c);
console.log(a==c); // 这个是相等的
console.log(Date(0));
console.log(Date(60000));
console.log(Date("a")); // 不论输入什么，输出都是 new Date();
console.log(new Date());
// 040
var min = Math.min(), max = Math.max();
console.log(min<max);
console.log(Math.min()); // Infinity
console.log(Math.max()); // -Infinity
// 041
function captureOne(re, str) {
console.log(re,re.lastIndex);
var match =re.exec(str);
console.log(match);
// console.log(match[1]);
return match && match[1];
}
var numRe = /num=(\d+)/g,
wordRe = /word=(\w+)/i,
a1 = captureOne(numRe, "num=1"),
a2 = captureOne(wordRe, "word=1"),
a3 = captureOne(numRe, "NUM=2"),
a4 = captureOne(wordRe, "WORD=2");
console.log([a1===a2,a3===a4]);
console.log(a1);
console.log(a2);
console.log(a3); // 有g选项，全文查找出现的所有pattern，注意其lastIndex属性；
console.log(a4);
// 042
var a = new Date("2014-03-19"),
b = new Date(2014,03,19);
console.log([a.getDay()===b.getDay(),a.getMonth()===b.getMonth()]);
// dateObj = new Date(year,month,date[,hours[,minutes[,seconds[,ms]]]])
// month 必选项。表示月份，从0到11之间的整数（1月至12月）
// getDay方法，返回Date对象中用本地时间表示的一周中的日期值，0至6之间的整数；
// 记忆：What day is today?
// 043
if('http://gifwrapped.com/picture.jpg'.match('.gif')){
console.log('a gif file');
}else{
console.log('not a gif file');
}
// String.prototype.match接受一个正则，如果不是，按照 new RegExp(obj)转化，所以.不会转义
// 044
function foo(a) {
var a;
return a;
}
function bar(a) {
var a = "bye";
return a;
}
console.log([foo('hello'),bar('hello')]);
var a = "a string";
var a; // 可以定义多次;
console.log(a);
*
*/
