JavaScript array is undefined | Example code

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Use length property with isArray() method to check an array is undefined in JavaScript.

if (!Array.isArray(array) || !array.length) {
  // array does not exist, is not an array, or is empty
  // ⇒ do not attempt to process array

Or do the check for undefined first, array empty or does not exist

if (array === undefined || array.length == 0) {
    // array empty or does not exist

Use Array some method to check array has an undefined value, it returns true if any item in the array is undefined.

JavaScript array is undefined

Simple example code.

<!DOCTYPE html>

    const arr = [1, 2, 3, 4, 5, 6, 7, 8, undefined, null, 0, "", -0];
    var res = arr.some(item => item === undefined);

    console.log("Array has undefined values",res)



JavaScript array is undefined

Filter undefined values from an array in Javascript

The filter() method creates a new array with all elements that pass the test implemented by the provided function. So, if x !== undefined, the object becomes part of the new array. If x === undefined, it is left out of the new array.

    const arr = [1, 2, 3, 4, 5, 6, 7, 8, undefined, null, 0, "", -0];
    const filter = arr.filter((x) => Boolean(x));

Output: [ 1, 2, 3, 4, 5, 6, 7, 8 ]

Do comment if you have any doubt or suggestions on this JS Array topic.

Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.

OS: Windows 10

Code: HTML 5 Version

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