JavaScript中filter的用法实例分析

var arr = [1, 2, 4, 5, 6, 9, 10, 15];
var r = arr.filter(function (x) {
  return x % 2 !== 0;
});
r; // [1, 5, 9, 15]

var arr = ['A', '', 'B', null, undefined, 'C', ' '];
var r = arr.filter(function (s) {
  return s && s.trim(); // 注意IE9以下的版本没有trim()方法
});
r; // ['A', 'B', 'C']

var arr = ['A', 'B', 'C'];
var r = arr.filter(function (element, index, self) {
  console.log(element); // 依次打印'A', 'B', 'C'
  console.log(index); // 依次打印0, 1, 2
  console.log(self); // self就是变量arr
  return true;
});

'use strict';
var
  r,
  arr = ['apple', 'strawberry', 'banana', 'pear', 'apple', 'orange', 'orange', 'strawberry'];
r = arr.filter(function (element, index, self) {
  return self.indexOf(element) === index;
});
console.log(r.toString());

'use strict';
function get_primes(arr) {
  var i;
  return arr.filter(function (element) {
      var flag=true;
      if(element<2){
      flag=false;
    }else {
      for(var i=2;i<element;i++){
        if (element%i==0){
          flag=false;
          break;
        }
      }
    }
    return flag;
  });
}
// 测试:
var
  x,
  r,
  arr = [];
for (x = 1; x < 100; x++) {
  arr.push(x);
}
r = get_primes(arr);
if (r.toString() === [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97].toString()) {
  console.log('测试通过!');
} else {
  console.log('测试失败: ' + r.toString());
}