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Javascript – what does this (h.hj=h.hj||function(){…..) syntax do?

Wanted to understand what does this below syntax do and what is it called.

h.hj=h.hj||function(){ (h.hj.q=h.hj.q||[]).push(arguments) };

Wanted to understand what purpose does h.hj=h.hj serve before the OR condition.

Want to understand the purpose of the syntax and why its written that way.

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2

Answers


  1. 0

    Wanted to understand what does this below syntax do and what is it
    called.

    h.hj = h.hj || function(){ (h.hj.q = h.hj.q || []).push(arguments) };

    It’s a Javascript expression. It assigns a function to an hj property on an object named h.

    Wanted to understand what purpose does h.hj = h.hj serve before the
    OR condition.

    h.hj = h.hj is regular assignment. If h.hj is truthy then h.hj is reassigned back to itself.

    Want to understand the purpose of the syntax and why its written that
    way.

    This overall looks to be an expression to assign a singleton function to h.hj (whatever that is) that pushes arguments into an h.hj.q array each time it’s called.

    The first time this is called h.hj is likely undefined, so the function callback is assigned. On subsequent calls since this h.hj function is defined, i.e. truthy, it’s simply reassigned back to itself.

    In the callback an h.hj.q array is created if it does not exist, and on each function call an arguments variable is pushed into the array.

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  2. 0

    I’ll break it down for you…

    h.hj=h.hj||function(){ (h.hj.q=h.hj.q||[]).push(arguments) };

    h should be defined before this expression. It should be a function or an object.

    h.hj = h.hj || function(){ ... } retains h.hj value if defined or, if undefined/falsy, defines it as function(){ ... }.

    Inside the function, h.hj should be the function itself (if not defined anywhere else). h.hj.q retains h.hj.q value if defined or, if undefined/falsy, defines it as [].

    Then the function just push the arguments given to the function into the h.hj.q which should be an array.

    The main behavior here is that the function attaches every parameter given in its calls to the q property of the function itself. Then, later you can recover all those parameters through the function object itself.

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