Underscore.js _.pickWhen() Method

The _.pickWhen() method returns a copy of the object containing those properties for which the given predicate function returns true. The predicate function is invoked with each property value.

Syntax:

_.pickWhen( Object_name, predicate_func );

Parameters:

• Object_name: Object from which the key/value pair is to be picked.
• predicate_func: Given function which contains the conditions for properties is to be picked

Return Value: This method returns a copy of the object after containing properties.

Note: This will not work in normal JavaScript because it requires the underscore.js contrib library to be installed. 

Underscore.js contrib library can be installed using npm install underscore-contrib –save.

Example 1:

Javascript

// Defining underscore contrib variable
var _ = require('underscore-contrib');

var obj = {
    1: "Gfg1",
    2: "Gfg2",
    3: "Gfg3"
};

var val = _.pickWhen(obj, function (id)
          { return id == "Gfg1" });
console.log(val);

Output:

{ '1': 'Gfg1' }

Example 2: If no property is found in the object, this method picks nothing.

Javascript

// Defining underscore contrib variable
var _ = require('underscore-contrib');

var obj = {
    1: "Gfg1",
    2: "Gfg2",
    3: "Gfg3"
};

var val = _.pickWhen(obj, function (id)
          { return id == "Gfg4" });
console.log(val);

Output:

{}