Underscore.js _.map() Function
The Underscore.js is a JavaScript library that provides a lot of useful functions that helps in the programming in a big way like the map, filter, invoke etc even without using any built-in objects.
The _.map() function is an inbuilt function in Underscore.js library of the JavaScript which is used to produce a new array of values by mapping each value in list through transformation function (iteratee). It displays the result as a list on the console. In this list the output of the first element, i.e, the element at index 0 has it’s result at index 0 of the returned list and when all the elements of the list are passed to the function/iteratee and no more elements remain then the _.map loop ends.
Syntax:
_.map(list, function)
Parameters: It accepts two parameters which are specified below-
- list: It is the list which contains some elements.
- function: It is the function which is executed by taking each element of the list.
Return values: It returns the object property value or array element value at the current position.
<html> <head> <script> underscore.js/1.9.1/underscore-min.js" > </script> <script type="text/javascript" /1.9.1/underscore-min.js.map"></script> <script type="text/javascript" /1.9.1/underscore.js"></script></head> <body> <script type="text/javascript"> _.map([1, 2, 3, 4], function(num){ return num * 2; }); </script></body> </html> |
Output:
<html> <head> <script> underscore.js/1.9.1/underscore-min.js" > </script> <script type="text/javascript" /1.9.1/underscore-min.js.map"></script> <script type="text/javascript" /1.9.1/underscore.js"></script></head> <body> <script type="text/javascript"> _.map( [1, 2, 3], function( num ) { for(var i=0;i<num;i++) var str="This is"; str+=i+1; str+="list item"; return(str); }); </script></body> </html> |
Output:
<html> <head> <script> underscore.js/1.9.1/underscore-min.js" > </script> <script type="text/javascript" /1.9.1/underscore-min.js.map"></script> <script type="text/javascript" /1.9.1/underscore.js"></script></head> <body> <script type="text/javascript"> _.map([[1, 2], [3, 4], [5, 6]], _.last); </script></body> </html> |
Output:
<html> <head> <script> underscore.js/1.9.1/underscore-min.js" > </script> <script type="text/javascript" /1.9.1/underscore-min.js.map"></script> <script type="text/javascript" /1.9.1/underscore.js"></script></head> <body> <script type="text/javascript"> var list = ['Geeks','for', 'Geeks', 'JS']; m = _.map(list, function (l) { return l + ' is mapped from a list.'; }); </script></body> </html> |
Output:
<html> <head> <script> underscore.js/1.9.1/underscore-min.js" > </script> <script type="text/javascript" /1.9.1/underscore-min.js.map"></script> <script type="text/javascript" /1.9.1/underscore.js"></script></head> <body> <script type="text/javascript"> _.map( [ 0, 7, 2, -1, 8 ], function( n ) { return n>=3 ? "greater" : "smaller"; }); </script></body> </html> |
Output:
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