Detailed explanation of how to use in_array function to determine array usage in JavaScript-JS Tutorial-php.cn

Detailed explanation of how to use in_array function to determine array usage in JavaScript

伊谢尔伦

Release： 2017-07-25 14:43:03

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In JS, there is no function that can be used directly to determine whether a value is in an array. For example, there is the in_array() function in PHP. But we can write a function like in_array() to determine whether a value is in the function.

/**
 * JS判断一个值是否存在数组中
 */
 
// 定义一个判断函数
var in_array = function(arr){
  // 判断参数是不是数组
  var isArr = arr && console.log(
      typeof arr===&#39;object&#39; ? arr.constructor===Array ? arr.length ? arr.length===1 ? arr[0]:arr.join(&#39;,&#39;):&#39;an empty array&#39;: arr.constructor: typeof arr 
    );
 
  // 不是数组则抛出异常
  if(!isArr){
    throw "arguments is not Array"; 
  }
 
  // 遍历是否在数组中
  for(var i=0,k=arr.length;i<k;i++){
    if(this==arr[i]){
      return true;  
    }
  }
 
  // 如果不在数组中就会返回false
  return false;
}
 
// 给字符串添加原型
String.prototype.in_array = in_array;
// 给数字类型添加原型
Number.prototype.in_array = in_array;
 
// 声明一个数组
var arr = Array(&#39;blue&#39;,&#39;red&#39;,&#39;110&#39;,&#39;120&#39;);
 
// 字符串测试
var str = &#39;red&#39;;
var isInArray = str.in_array(arr);
alert(isInArray); // true
 
// 数字测试
var num = 119;
var isInArray = num.in_array(arr);
alert(isInArray); // false

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If the input is not an array, an exception will be thrown.

/**
 * JS判断一个值是否存在数组中
 */
 
// 定义一个判断函数
var in_array = function(arr){
  // 判断参数是不是数组
  var isArr = arr && console.log(
      typeof arr===&#39;object&#39; ? arr.constructor===Array ? arr.length ? arr.length===1 ? arr[0]:arr.join(&#39;,&#39;):&#39;an empty array&#39;: arr.constructor: typeof arr 
    );
 
  // 不是数组则抛出异常
  if(!isArr){
    throw "arguments is not Array"; 
  }
 
  // 遍历是否在数组中
  for(var i=0,k=arr.length;i<k;i++){
    if(this==arr[i]){
      return true;  
    }
  }
 
  // 如果不在数组中就会返回false
  return false;
}
 
// 给字符串添加原型
String.prototype.in_array = in_array;
// 给数字类型添加原型
Number.prototype.in_array = in_array;
 
// 声明一个数组
var arr = null;
 
// 字符串测试
var str = &#39;red&#39;;
var isInArray = str.in_array(arr);
alert(isInArray); // uncaught exception: arguments is not Array

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will report an error directly.

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