What does _(variable_name) mean in javascript?

Question

I came across the following javascript code:

this.removeEdge = function(source, target) {   if(!_states[source]) return;    var children = _states[source].children,       index = _(children).indexOf(target);   if(index !== -1) children.splice(index, 1); }; 

What does _(children) mean?

Answer 1

_ is a valid variable identifier in JavaScript, and could theoretically refer to anything. Using _(...) with function syntax implies that _ is a function.

That said, it is commonly used by the underscore.js library, however if you're looking at minified code, it's quite possibly being used as another single-character variable name to save on file size.

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In your example provided, it appears that underscore.js is being used to treat children as a collection, so that the indexOf function can be applied to the collection. This would be similar to calling:

_.indexOf(children, target);