js的6道基础题（笔试常考题）

js的6道基础题（笔试常考题）。

题目一：找出数字数组中最大的元素

var arr=[0,1,2,3,4,5,6,7,8,9];
console.log(math.max.apply(null,arr))

题目二：转化一个数字数组为function数组（每个function都弹出相应的数字）

for循环闭包的问题

var arr=[0,1,2,3,4,5,6,7,8,9],arrfunc = [];
for(var i = 0, l = arr.length; i < l; i++){
  arrfunc.push((function(i) {
    return function() {
      console.log(arr[i]);
    }
  })(i))
}

题目三：给object数组进行排序（排序条件是每个元素对象的属性个数）

object.prototype.mylength = function(){
  var length = 0;
  for(var i in this){
    length ++;
  }
  return length;
}
var objarr = [
  {a:1, b:2, c:5, d:7, e:8, g:0, h:12, i:5, v:9, w:9, x:9, y:9, z: 15},
  {a:2, b:2, c:5, d:7, e:8, g:0, h:12, i:5, j:7, k:5, l:9, m:9, n:0, o:1, p:9, x:9, y:9, z:9 }, 
  {a:3, b:2, c:5, d:7, e:8, g:0, h:12, i:5, j:7, k:5, l:9, m:9, n:0, o:1, p:9, q:0 },
  {a:4, b:2, c:5, d:7, e:8, g:0, h:12, i:5, j:7, k:5, w:9, x:9, y:9, z:9 },
  {a:5, b:2, c:5, d:7, e:8, g:0, h:12, i:5, j:7, k:5, v:9, w:9, x:9, y:9, z:9 },
  {a:6, b:2, c:5, d:7, e:8, g:0, h:12, i:5, j:7, k:5, l:9, m:9, n:0, o:1, p:9, q:0, r:8, s:9, t:9, z:9 },
  {a:7, b:2, c:5, d:7, e:8, x:9, y:9, z:9 }
];
// arr before sort
var numarr1 = []
for(var i = 0, l = objarr.length; i < l; i++ ){
  numarr1.push( objarr[i].mylength() )
}
console.log(numarr1.join(" ")) //result
// arr after sort
objarr.sort(function(a,b){
  // stable sort
  // return (a.mylength() > b.mylength()) === true? 1:-1;
  // unstable sort
  return (a.mylength() >= b.mylength()) === true? 1:-1;
  // return a.mylength() - b.mylength();
})
var numarr2 = []
for(var i = 0, l = objarr.length; i < l; i++ ){
  // console.log(i,l,objarr[i].mylength());
  numarr2.push( objarr[i].mylength() )
}
console.log(numarr2.join(" ")) //result

题目四：利用javascript打印出fibonacci数（不使用全局变量）

var fibonacci = (function(){
  var s = [];
  var fun = function(x) {
    if(s[x]){
      return s[x];
    }
    if(x < 0) {
      throw "can‘t be negative";
      return ;
    }
    else if(x === 0 || x === 1) {
      s[x] = s[x] || x;
      return s[x];
    }
    else{
      s[x] = ( fun(x - 1) + fun(x - 2) );
      return s[x];
    }
  };
  fun.print = function() {
    console.log(s.join(" "));
  }
  fun.printlast = function() {
    // console.log(s.length);
    return(s[s.length-1]);
  }
  window.s = s;
  return fun;

})()
console.time(200);
console.log(fibonacci(200));
console.log(fibonacci.printlast());
console.log(fibonacci.print());
console.timeend(200);

var fibonacci2 = function(x){
  if(x < 0) {
    throw "can‘t be negative";
    return ;
  }
  if(x === 0 || x === 1) {
    return x;
  }
  var num = ( fibonacci2(x - 1) + fibonacci2(x - 2) )
  return num;
}
console.time(32);
console.log(fibonacci2(32));
console.timeend(32);

题目五：实现如下语法的功能：var a = (5).plus(3).minus(6);

number.prototype.plus = function(x) {
  var num = this.valueof() + x;
  return number(num);
}
number.prototype.minus = function(x) {
  var num = this.valueof() - x;
  return number(num);
}

var a = (5).plus(3).minus(6);
console.log(a);
alert(a);

题目六：实现如下语法的功能：var a = add(2)(3)(4);

function add(x) {
  var mid;
  mid = x || 0;
  function addobj(x) {
    x = x || 0;
    mid = mid + x;
    return addobj;
  }
  addobj.valueof = function() {
    return mid;
  }
  addobj.tostring = function() {
    return mid;
  }
  return addobj;
}
//call the obj.valueof function
console.log(add(2));
console.log(add(2)(3));
console.log(add(2)(3)(4));
console.log(add(2)(3)(4)(5));

//call the obj.tostring function
alert(add(2));
alert(add(2)(3));
alert(add(2)(3)(4));
alert(add(2)(3)(4)(5));