JavaScript - get array element fulfilling a condition

Question

I\'m learning JavaScript using W3C and I didn\'t find an answer to this question.

I\'m trying to make some manipulations on array elements which fulfill some conditi

Answer 1

Write a generic function that accepts various conditions:

function array_only(arr, condition) {
    hold_test=[]
    arr.map(function(e, i) {if(eval(condition)){hold_test.push(e)}})
    return(hold_test)
    }

Example:

use_array = ['hello', 'go_there', 'now', 'go_here', 'hello.png', 'gogo.log', 'hoho.png']

Usage:

return only elements containing .log extension:

array_only(use_array, "e.includes('.log')")

[ 'gogo.log' ]

return only elements containing .png extension:

array_only(use_array, "e.includes('.png')")

[ 'hello.png', 'hoho.png' ]

return only elements NOT containing .png extension:

array_only(use_array, "!e.includes('.png')")

[ 'hello', 'go_there', 'now', 'go_here', 'gogo.log' ]

return elements containing set of extensions and prefixes:

array_only(use_array, "['go_', '.png', '.log'].some(el => e.includes(el))")

[ 'go_there', 'go_here', 'hello.png', 'gogo.log', 'hoho.png' ]

You can easily pass MULTIPLE CONDITIONS

return all png files that are less than 9 characters long:

array_only(use_array, "e.includes('.png') && e.length<9")

[ 'hoho.png' ]

Answer 2

Just came across the same problem. Tim Down came close, he just needed a wrapper to the length of the filtered array:

// count elements fulfilling a condition
Array.prototype.count = function (f) {
  return this.filter(f).length;  
};

Usage:

// get the answer weight from the question's values array
var w = Math.pow(q.values.count(function(v) { return v !== -1; }), -1);

I hope that answers this long standing question!

Answer 3

You can use for ... in in JavaScript:

for (var key in array) {
    if (/* some condition */) {
        // ...
    }
}

As of JavaScript 1.6, you can use this, too:

for each (var element in array) {
    // ...
}

These are mainly meant to traverse object properties. You should consider to simply use your for-loop.

EDIT: You could use a JavaScript framework like jQuery to eliminate these cross-browser problems. Give it a try. Its $.each()-method does the job.

Answer 4

Problem:

I need to know if a client set exists for any PJ client.

Solution:

function deveExibirLista(lst: Clientes[]){
    return lst.some(cli => cli.Documento === 14);
}

It's return boolean

Answer 5

You can use Array.prototype.find, wich does exactly what you want, returns the first element fullfilling the condition. Example:

> ([4, {a:7}, 7, {a:5, k:'r'}, 8]).find(o => o.a == 5)

{a:5, k:'r'}

Answer 6

In most browsers (not IE <= 8) arrays have a filter method, which doesn't do quite what you want but does create you an array of elements of the original array that satisfy a certain condition:

function isGreaterThanFive(x) {
     return x > 5;
}

[1, 10, 4, 6].filter(isGreaterThanFive); // Returns [10, 6]

Mozilla Developer Network has a lot of good JavaScript resources.