数组之ES5 方法 实现

    var arr = [1,2,3,4,5];

    arr.forEach(function(curval, index, array) {
      var squ = curval * curval;
      console.log('index is : ' + index + ', result is : ' + squ);
    })

    var mul2 = function(num) {
      return num * 2;
    }

    var mapArr = arr.map(mul2);
    console.log(mapArr);  // [2,4,6,8,10]

    var evenArr = function(num) {
      return num % 2 === 0;
    }

    var filterArr = arr.filter(evenArr);
    console.log(filterArr);  // [2,4]

    var everyArr = arr.every(evenArr);
    console.log(everyArr);  // false

    var someArr = arr.some(evenArr);
    console.log(someArr);  // true

    var findArr = arr.find(evenArr);
    console.log(findArr);  // 2

    var findIndexArr = arr.findIndex(evenArr);
    console.log(findIndexArr);  // 1

    var maxVal = function(lastVal, curVal) {
      return lastVal > curVal ? lastVal : curVal;
    }

    var reduceArr = arr.reduce(maxVal);
    console.log(reduceArr);  // 5