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JavaScript: Check whether the provided argument is array-like

JavaScript fundamental (ES6 Syntax): Exercise-205 with Solution

Write a JavaScript program to check whether the provided argument is array-like (i.e. is iterable).

  • Check if the provided argument is not null and that its Symbol.iterator property is a function.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const isArrayLike = val => {
  try {
    return [...val], true;
  } catch (e) {
    return false;
  }
};
console.log(isArrayLike(document.querySelectorAll('.className'))); // true
console.log(isArrayLike('abc')); // true
console.log(isArrayLike(null)); // false

Sample Output:

true
true
false

Flowchart:

flowchart: Check whether the provided argument is array-like.

Live Demo:

See the Pen javascript-basic-exercise-205-1 by w3resource (@w3resource) on CodePen.


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Previous: Write a JavaScript program that will check whether the given argument is a native boolean element.
Next: Write a JavaScript program to check if a given string is an anagram of another string (case-insensitive, ignores spaces, punctuation and special characters).

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JavaScript: Tips of the Day

Checking if a key exists in a JavaScript object?

Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined?

var obj = { key: undefined };
obj["key"] !== undefined // false, but the key exists!

You should instead use the in operator:

"key" in obj // true, regardless of the actual value

If you want to check if a key doesn't exist, remember to use parenthesis:

!("key" in obj) // true if "key" doesn't exist in object
!"key" in obj   // ERROR!  Equivalent to "false in obj"

Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty:

obj.hasOwnProperty("key") // true

Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined? var obj = { key: undefined }; obj["key"] !== undefined // false, but the key exists! You should instead use the in operator: "key" in obj // true, regardless of the actual value If you want to check if a key doesn't exist, remember to use parenthesis: !("key" in obj) // true if "key" doesn't exist in object !"key" in obj // ERROR! Equivalent to "false in obj" Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty: obj.hasOwnProperty("key") // true For performance comparison between the methods that are in, hasOwnProperty and key is undefined.

Ref: https://bit.ly/2CFNp1X