The Lodash documentation says that it supports lazy evaluation. From my testing, the below chain is being evaluated 100 times rather than 10. I'm using version 3.10.1.

_(_.range(100))
 .map(function(x) {console.log(1); return x; })
 .take(10)
 .value()

You can see that we print to the console 100 times inside map, rather than the 10 times I would have expected. Check out the problem here: /

What am I doing wrong? How can I make this evaluate lazily?

Update: This appears to be a regression in Lodash. I tested how this works across versions and came across the following results:

Version 2.4.2: 100 times /

Version 3.0.0: 10 times /

Version 3.9.0 10 times /

Version 3.10.0: 100 times /

The Lodash documentation says that it supports lazy evaluation. From my testing, the below chain is being evaluated 100 times rather than 10. I'm using version 3.10.1.

_(_.range(100))
 .map(function(x) {console.log(1); return x; })
 .take(10)
 .value()

You can see that we print to the console 100 times inside map, rather than the 10 times I would have expected. Check out the problem here: https://jsfiddle/07utwk6y/

What am I doing wrong? How can I make this evaluate lazily?

Update: This appears to be a regression in Lodash. I tested how this works across versions and came across the following results:

Version 2.4.2: 100 times https://jsfiddle/4Lq7z5xL/

Version 3.0.0: 10 times https://jsfiddle/fd6g6un5/

Version 3.9.0 10 times https://jsfiddle/ju8rppee/

Version 3.10.0: 100 times https://jsfiddle/x1g13oo8/

• javascript
• lodash

1 Answer 1

This is expected behavior. Lodash will only perform this optimization on arrays with 200 or more items. Increase the range to 200 in the first line to see this working.