What Is the Equivalent of Array. Any? in Javascript?
I'm Looking for a Method for Javascript That Returns True or False When It's Empty. .. Something Like Ruby Any? or Empty? []. Any? #=> False []. Empty? #=>...
I'm looking for a method for JavaScript that returns true or false when it's empty... something like Ruby any? or empty?
[].any? #=> false
[].empty? #=> true
11 Answers
The JavaScript native .some() method does exactly what you're looking for:
function isBiggerThan10(element, index, array) {
return element > 10;
}
[2, 5, 8, 1, 4].some(isBiggerThan10); // false
[12, 5, 8, 1, 4].some(isBiggerThan10); // true
JavaScript has the Array.prototype.some() method:
[1, 2, 3].some((num) => num % 2 === 0);
returns true because there's (at least) one even number in the array.
In general, the Array class in JavaScript's standard library is quite poor compared to Ruby's Enumerable. There's no isEmpty method and .some() requires that you pass in a function or you'll get an undefined is not a function error. You can define your own .isEmpty() as well as a .any() that is closer to Ruby's like this:
Array.prototype.isEmpty = function() {
return this.length === 0;
}
Array.prototype.any = function(func) {
return this.some(func || function(x) { return x });
}
Libraries like underscore.js and lodash provide helper methods like these, if you're used to Ruby's collection methods, it might make sense to include them in your project.
I'm a little late to the party, but...
[].some(x => !!x)
var a = [];
a.length > 0
I would just check the length. You could potentially wrap it in a helper method if you like.
I believe this to be the cleanest and readable option:
var empty = [];
empty.some(x => x); //returns false
JavaScript arrays can be "empty", in a sense, even if the length of the array is non-zero. For example:
var empty = new Array(10);
var howMany = empty.reduce(function(count, e) { return count + 1; }, 0);
The variable "howMany" will be set to 0, even though the array was initialized to have a length of 10.
Thus because many of the Array iteration functions only pay attention to elements of the array that have actually been assigned values, you can use something like this call to .some() to see if an array has anything actually in it:
var hasSome = empty.some(function(e) { return true; });
The callback passed to .some() will return true whenever it's called, so if the iteration mechanism finds an element of the array that's worthy of inspection, the result will be true.
If you really want to got nuts, add a new method to the prototype:
if (!('empty' in Array.prototype)) {
Array.prototype.empty = function () {
return this.length === 0;
};
}
[1, 2].empty() // false
[].empty() // true
Just use Array.length:
var arr = [];
if (arr.length)
console.log('not empty');
else
console.log('empty');
See MDN
What you want is .empty not .empty() to fully mimics Ruby :
Object.defineProperty( Array.prototype, 'empty', {
get: function ( ) { return this.length===0 }
} );
then
[].empty //true
[3,2,8].empty //false
For any , see my answer here
Array has a length property :
[].length // 0
[0].length // 1
[4, 8, 15, 16, 23, 42].length // 6
polyfill* :
Array.prototype.any=function(){
return (this.some)?this.some(...arguments):this.filter(...arguments).reduce((a,b)=> a || b)
};
If you want to call it as Ruby , that it means .any not .any(), use :
Object.defineProperty( Array.prototype, 'any', {
get: function ( ) { return (this.some)?this.some(function(e){return e}):this.filter(function(e){return e}).reduce((a,b)=> a || b) }
} );
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`* :
James Sterling reports on renewable energy developments, climate policy, ecological conservation, and green tech innovations around the globe.
