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How to check if a JavaScript variable is an array or an object?

Dennis Thomas

Dennis Thomas
7y
2.3k
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    Dennis Thomas
    Thank you Dang Dang for the post. jQuery, $.isArray() uses Array.isArray() JavaScript method. But it is not supported by older browsers.
    Dennis Thomas
    7y
    2
    Đặng Đang
    simply using $.isArray()
    Đặng Đang
    7y
    2
    Dennis Thomas
    Since a JavaScript Array is an object, typeof operator will return object for an array. So we cannot use that in this case.We can use Array.isArray() in browsers that support ECMAScript 5.Array.isArray(myArray); // returns trueBut older versions of browsers doesn't support ECMAScript 5. So, you need to write your own function for this. You can check the prototype of the object to search for the word "Array".function isArray(myVar) {return myVar.constructor.toString().indexOf("Array") > -1; }The above function will return true if the parameter is an array.
    Dennis Thomas
    7y
    2
    Gajendra Jangid
    using $.isArray()
    Gajendra Jangid
    7y
    1
    Jin Necesario

    Two ways to check if an Array

    1. Using the Object.prototype.toString.call([]).
    2. Using the Array.isArray([]).

    Code Samples Below: 

    1. const programmingLanguages = ['C#', 'JavaScript', 'Java'];
    3. //old way
    4. console.log(Object.prototype.toString.call(programmingLanguages) === '[object Array]'); //output: true
    6. //new way
    7. console.log(Array.isArray(programmingLanguages)); //output: true

    To check if object you can use the typeof operator and check if it is not equal to null. The reason you need to check if not null is because null when passed into the typeof operator returns an “object” result.

    1. const customer = {};
    3. console.log(typeof(customer)); //output: object; 
    5. //but it is better to check if typeof object and not null
    6. console.log(typeof(customer) === "object" && customer !== null); //output: true
    8. const product = null;
    10. //but it is better to check if typeof object and not equal to null
    11. console.log(typeof(product) === "object" && product !==null); //output: false
    Jin Necesario
    5y
    0
    Bidyasagar Mishra

    $.isArray()

    Bidyasagar Mishra
    6y
    0
    Neeraj Negi
    let obj ={}; let arr = [];check output of console.log in each variable and you can see that they have different proto.console.log(obj.constructor.prototype.hasOwnProperty('push')); // this will give false because and object don't have a push method where as an array have the push method. console.log(arr.constructor.prototype.hasOwnProperty('push')); // will return true
    Neeraj Negi
    7y
    0
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