w3resource

JavaScript: Return true if the provided predicate function returns true for at least one element in a collection, false otherwise

JavaScript fundamental (ES6 Syntax): Exercise-255 with Solution

Write a JavaScript program that will return true if the provided predicate function returns true for at least one element in a collection, false otherwise.

  • Use Array.prototype.some() to test if any elements in the collection return true based on fn.
  • Omit the second argument, fn, to use Boolean as a default.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const any = (arr, fn = Boolean) => arr.some(fn);
console.log(any([0, 1, 2, 0], x => x >= 2));
console.log(any([0, 0, 1, 0]));

Sample Output:

true
true

Flowchart:

flowchart: Return true if the provided predicate function returns true for at least one element in a collection, false otherwise.

Live Demo:

See the Pen javascript-basic-exercise-255-1 by w3resource (@w3resource) on CodePen.


Improve this sample solution and post your code through Disqus

Previous: Write a JavaScript program to generate a UUID in Node.JS. Use crypto API to generate a UUID, compliant with RFC4122 version 4.
Next: Write a JavaScript program to check if two given numbers are approximately equal to each other.

What is the difficulty level of this exercise?

Test your Programming skills with w3resource's quiz.



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