How to Check if All Values are True in a JavaScript Array

If you ever need to check if an array only has true values in JavaScript, you can use Array.every in combination of the global Boolean object:

const validations = [
    true,
    false,
    '0',
    undefined
    null
];

const isEntirelyTrue = validations.every(Boolean);

// The above is equivalent to saying:
const isEntirelyTrue = validations.every(item => !!item);
const isEntirelyTrue = validations.every(item => item === true);

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Explanation

The every method tests whether all elements in the array pass the test that is implemented in the callback function. It is exactly what we need for this purpose. It always returns a boolean value: either true or false.

Combining this with the global Boolean, which is a wrapper for boolean values, we can get the desired effect. It returns false if the value is one of:

[0, -0, null, false, NaN, undefined, '']

Any other value will produce true. It is equivalent of double negating a value to cast it to a boolean value, or comparing it to the boolean true.

Why Do You Need to Know About Functional Programming?The programming paradigm that simplifies your codeJust like object-oriented programming, functional programming has its own concepts too. Learn how you can apply them to JavaScript to make your code better.Learn More

Resources:

• Documentation for Array.prototype.every - MDN
• The global Boolean object - MDN