Underscore.js _.iterators.mapcat() Method

With the help of _.iterators.mapcat() method, we can get the function iterator which when called return the value which is  flattening the contents of iterator and combined with the unary function by using this method.

Syntax:

_.iterators.mapcat(iter, unaryFn)

Parameters: This method accepts two parameter as mentioned above and described below: 

• iter: This parameter holds the iterator list of the array.
• unaryFn: This parameter holds the unary function key.

Return value: Return the function iterator which generate the value by mapping with unaryFn.

Note: To execute the below examples, you have to install the underscore-contrib library by using this command prompt we have to execute the following command.

npm install underscore-contrib

Below example illustrate the Underscore.js _.iterators.mapcat() method in JavaScript:

Example 1: In this example, we can see that by using _.iterators.mapcat() method, we are able to get the function iterator which can generate the value after mapping with the unary function by using this method.

Javascript

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

function generateNumber (x)  {
    return _.iterators.List(_.range(1, x));
}

var treeIter = _.iterators.Tree([2, [3]]);

var geek = _.iterators.mapcat(treeIter, generateNumber);

geek();
geek();
geek();

Output :

1
1
2

Example 2:

Javascript

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

function generateNumber (x)  {
    return _.iterators.List(_.range(x));
}

var treeIter = _.iterators.Tree([[2, 1], [1, 3]]);

var geek = _.iterators.mapcat(treeIter, generateNumber);

for(var i = 0; i < 5; i++) {
    console.log(geek());
}

Output:

0
1
0
0
0