Lodash _.every() Method

Syntax, Parameter and Return Value

Syntax: 

_.every(collection, [predicate=_.identity])

Parameters:

• collection (Array|Object): The collection to iterate over.
   
• [predicate=_.identity] (Function): The function invoked per iteration.

Return Value: 

(boolean) - Returns true if all elements pass the predicate check, else false.

Examples 

Checking All Numbers for Evenness:

• JavaScript

JavaScript

var _ = require('lodash');

var numbers = [2, 4, 6, 8, 10];

var allEven = _.every(numbers, n => n % 2 === 0);

console.log(allEven); 

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Output: 

true

This example demonstrates checking if all numbers in an array are even.

Validating Object Properties:

• JavaScript

JavaScript

var users = [{ 'user': 'barney', 'age': 36, 'active': false },

             { 'user': 'fred',   'age': 40, 'active': false }];

var allInactive = _.every(users, {'active': false});

console.log(allInactive); 

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Output:

 true

Here, _.every() is used to verify if all objects in an array have a specific property value.

Array of Strings:

• JavaScript

JavaScript

var words = ['apple', 'amber', 'arc'];

var allStartWithA = _.every(words, w => w.startsWith('a'));

console.log(allStartWithA); 

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Output: 

true

Checks if every string in an array starts with the letter 'a'.

Using Function Shorthand:

• JavaScript

JavaScript

var objects = [{ 'n': 4 }, { 'n': 6 }, { 'n': 8 }];

var allGreaterThanThree = _.every(objects, 'n', n => n > 3);

console.log(allGreaterThanThree); 

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Output:

 true

Utilizing Lodash's shorthand syntax for cleaner and more concise code.

Frequently Asked Questions 

How does _.every() behave with an empty collection?

_.every() returns true for empty collections as there are no elements to fail the predicate test, adhering to the principle of vacuous truth.

Can _.every() work with collections containing different data types?

Yes, but the predicate function must be capable of handling the various data types present in the collection.

Is _.every() efficient for large datasets?

_.every() is efficient for most datasets, but its performance depends on the complexity of the predicate function and the size of the dataset.

Conclusion

Lodash's _.every() method is a concise and effective tool for verifying that all elements in a collection meet a specific criterion. It simplifies the process of uniform condition checking, enhancing both the readability and the reliability of code. This method is an excellent example of how Lodash facilitates more expressive and efficient JavaScript programming.

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