Never use a dependency that you could replace with an afternoon of programming

Re:Never use a dependency that you could replace with an aft... by ghj on Tuesday August 11, 2020 @05:28PM (#24126183)

I highly doubt js engines would compile a string down to a linked list. But you're right they might compile it to a circular buffer or deque which can have O(1) prepends.

Quick googling shows that this optimization might exist but only for firefox and only if you use "unshift": https://lannonbr.com/blog/2020-01-27-shift-optimizations https://jandemooij.nl/blog/2017/12/06/some-spidermonkey-opti...

But it's very unlikely that the jit can optimize `str = ch + str;`

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Re:Never use a dependency that you could replace with an aft... by cogman10 on Tuesday August 11, 2020 @07:00PM (#24126956)

Depends on the form that `str = ch + str` takes inside the loop. But yeah, the way they wrote the code makes it less likely to work well.

    let padding = '';
    for (let i = 0; i < len; ++i)
      padding += ch;
    return padding + str;

The above would probably get caught by the JIT and would essentially be optimized to what `ch.repeat(len) + str;` would do.

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