javascript - Array splicing with coffeescript, what is _ref for? - Stack Overflow

In the CoffeeScript docs for array splicing, what is the purpose of the trailing , _ref?

CoffeeScript:

numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
numbers[3..6] = [-3, -4, -5, -6]

Compiles to:

var numbers, _ref;
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
[].splice.apply(numbers, [3, 4].concat(_ref = [-3, -4, -5, -6])), _ref;

In the CoffeeScript docs for array splicing, what is the purpose of the trailing , _ref?

CoffeeScript:

numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
numbers[3..6] = [-3, -4, -5, -6]

Compiles to:

var numbers, _ref;
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
[].splice.apply(numbers, [3, 4].concat(_ref = [-3, -4, -5, -6])), _ref;

• javascript
• coffeescript
• apply
• array-splice

Share Improve this question Follow asked Jul 28, 2012 at 11:06 AJPAJP 28.7k2626 gold badges9494 silver badges144144 bronze badges

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1 Answer 1

Sorted by: Reset to default 7

That's because CoffeeScript's slicing operation wants to return the slice it has just assigned, but splice() returns the removed elements instead.

So, in order to achieve this, it piles the construct into a code fragment that first assigns the slice to a local _ref variable, then uses the ma operator to return that variable after calling splice().