JavaScript: Check whether the provided value is of the specified type

JavaScript fundamental (ES6 Syntax): Exercise-208 with Solution

Check Specified Type

Write a JavaScript program to check whether the provided value is of the specified type.

• Ensure the value is not undefined or null using Array.prototype.includes().
• Compare the constructor property on the value with type to check if the provided value is of the specified type.

Sample Solution:

JavaScript Code:

// Define a function 'is' that checks if the provided value is an instance of the specified type
const is = (type, val) => ![, null].includes(val) && val.constructor === type;

// Test cases to check if the provided values are instances of the specified types
console.log(is(Array, [1])); // true (Array instance)
console.log(is(ArrayBuffer, new ArrayBuffer())); // true (ArrayBuffer instance)
console.log(is(Map, new Map())); // true (Map instance)
console.log(is(RegExp, /./g)); // true (RegExp instance)
console.log(is(Set, new Set())); // true (Set instance)
console.log(is(WeakMap, new WeakMap())); // true (WeakMap instance)
console.log(is(WeakSet, new WeakSet())); // true (WeakSet instance)
console.log(is(String, '')); // true (String instance)
console.log(is(String, new String(''))); // true (String instance)
console.log(is(Number, 1)); // true (Number instance)
console.log(is(Number, new Number(1))); // true (Number instance)
console.log(is(Boolean, true)); // true (Boolean instance)
console.log(is(Boolean, new Boolean(true))); // true (Boolean instance)

Output:

true
true
true
true
true
true
true
true
true
true
true
true
true

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-208-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that checks if a provided value is of a specified type using typeof and constructor comparisons.
• Write a JavaScript function that accepts a value and a type string, then returns true if the value matches that type.
• Write a JavaScript program that validates an input’s type against a given string such as "string", "number", or "object".
• Write a JavaScript function that uses Object.prototype.toString to check if a value is of the specified type.

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