JavaScript to determine whether a value in the array does not directly use the _ Basics

In JS to determine whether a value in the array and no function directly use, such as PHP has In_array () this function. But we can write a similar in_array () function to determine whether a value is in a function

Example 1

Copy Code code as follows:

/*
*
* Determine if a given variable value is included in the array
Parameters
* Needle: The value to be queried
* Haystack: Array of queries
* In haystack query needle exists, if found returns True, otherwise return false.
* This function can only be valid for characters and numbers
*
*/

function FindNum () {
var a=[1,2];//assuming that a is an array, obj is the number to judge
var obj=1;
var B = false;
for (var i = 0; i < a.length; i++) {
if (a[i] = = obj) {
b = true;break;
}
}
if (b)
Alert ("An array exists a[" + i + "]:" + a[i]);
Else
Alert ("+obj" does not exist in the array);
}

Example 2

Copy Code code as follows:

/**
* JS to determine whether a value exists in the array
* Jones Taiwan Blog
*/

Define a judgment function
var in_array = function (arr) {
Determines whether the parameter is an array
var Isarr = arr && Console.log (
typeof arr=== ' object '? Arr.constructor===array? Arr.length? Arr.length===1? Arr[0]:arr.join (', '): ' An empty array ': arr.constructor:typeof arr
);

Throw an exception if it is not an array
if (!isarr) {
Throw "arguments is not Array";
}

Traversal is in the array
for (Var i=0,k=arr.length;i<k;i++) {
if (This==arr[i]) {
return true;
}
}

Returns False if it is not in the array
return false;
}

To add a prototype to a string
String.prototype.in_array = In_array;
To add a prototype to a numeric type
Number.prototype.in_array = In_array;

Declaring an array
var arr = Array (' Blue ', ' red ', ' 110 ', ' 120 ');

String test
var str = ' red ';
var Isinarray = Str.in_array (arr);
alert (Isinarray); True

Digital test
var num = 119;
var Isinarray = Num.in_array (arr);
alert (Isinarray); False
Throws an exception if the passed-in is not an array
/**
* JS to determine whether a value exists in the array
* Jones Taiwan Blog
*/

Define a judgment function
var in_array = function (arr) {
Determines whether the parameter is an array
var Isarr = arr && Console.log (
typeof arr=== ' object '? Arr.constructor===array? Arr.length? Arr.length===1? Arr[0]:arr.join (', '): ' An empty array ': arr.constructor:typeof arr
);

Throw an exception if it is not an array
if (!isarr) {
Throw "arguments is not Array";
}

Traversal is in the array
for (Var i=0,k=arr.length;i<k;i++) {
if (This==arr[i]) {
return true;
}
}

Returns False if it is not in the array
return false;
}

To add a prototype to a string
String.prototype.in_array = In_array;
To add a prototype to a numeric type
Number.prototype.in_array = In_array;

Declaring an array
var arr = null;

String test
var str = ' red ';
var Isinarray = Str.in_array (arr);
alert (Isinarray); Uncaught exception:arguments is not Array
JS determines whether there is a duplicate value in an array
var ary = new Array ("111", "22", "33", "111");
var s = ary.join (",") + ",";
for (Var i=0;i<ary.length;i++) {
if (S.replace (ary[i]+ ",", ""). IndexOf (ary[i]+ ",") >-1) {
Alert ("There are repeating elements in the array:" + ary[i]);
Break
}
}

Example 5

Copy Code code as follows:

function Isrepeat (arr) {
var hash = {};
for (var i in arr) {
if (Hash[arr[i]])
return true;
Hash[arr[i]] = true;
}
return false;
}