Truth check all values in a JavaScript array

As mentioned in a previous article, JavaScript uses type coercion in Boolean contexts, such as conditionals. This means that values are considered either truthy or falsy depending on how they are evaluated in a Boolean context. Combining this with the Boolean function and truth checking a collection of values becomes a breeze.

Check if all values in an array are truthy

Using Array.prototype.every(), we can easily check if all values in an array are truthy. The Boolean function can be used as a default callback to check if all values are truthy, but specifying a custom callback function is also possible.

const all = (arr, fn = Boolean) => arr.every(fn);

all([4, 2, 3], x => x > 1); // true
all([1, 2, 3]); // true

Check if any values in an array are truthy

Using Array.prototype.some(), we can check if any values in an array are truthy. The Boolean function can be used as a default callback to check if any values are truthy, but specifying a custom callback function is also possible.

const any = (arr, fn = Boolean) => arr.some(fn);

any([0, 1, 2, 0], x => x >= 2); // true
any([0, 0, 1, 0]); // true

Check if all values in an array are falsy

Similarly, Array.prototype.some() can be used to check if any values in an array are falsy. Again, the Boolean function can be used as the default callback, but you can also specify a custom callback function.

const none = (arr, fn = Boolean) => !arr.some(fn);

none([0, 1, 3, 0], x => x == 2); // true
none([0, 0, 0]); // true

Check if all objects have a given property

Taking this one step further, Array.prototype.every() can be used to check if all objects in an array have a given property. This is useful for validating data, for example. Simply checking for the existence of a property will return a truthy or falsy value depending on whether the property exists or not.

const truthCheckCollection = (collection, pre) =>
  collection.every(obj => obj[pre]);

truthCheckCollection(
  [
    { user: 'Tinky-Winky', sex: 'male' },
    { user: 'Dipsy', sex: 'male' },
  ],
  'sex'
); // true