Why is Function.prototype.bind slow?-JavaScript中文网-JavaScript教程资源分享门户

Raynos提出了一个问题：Why is Function.prototype.bind slow?，或许与您遇到的问题类似。

回答者Domenic给出了该问题的处理方式：

Based on http://jsperf.com/bind-vs-emulate/6, which adds the es5-shim version for comparison, it looks like the culprit is the extra branch and instanceof that the bound version has to perform to test if it's being called as a constructor.

Each time the bound version is run, the code that gets executed is essentially:

-- ----- ---------- ------ -
    -- ----- -------- --- --- ------------ ----- --- ------ ---------- --- - ----
- ---- -
    ------ -------------
     -----
     ----------------------------------
    --

    -- ---- -- -- -- ---- -----
    -- -- --- ---- ---
    -- - ---------- ------- --------- ------ -- ------- ------
    -- - --------- --- ----- -------
-

In the V8 source code, this check appears (inside boundFunction) as

-- --------------------- -
    ------ -----------------------------------
-

(Plaintext link to v8natives.js for when Google Code Search dies.)

It is a bit puzzling that, for Chrome 16 at least, the es5-shim version is still faster than the native version. And that other browsers have rather varying results for es5-shim vs. native. Speculation: maybe %_IsConstructCall() is even slower than this instanceof bound, perhaps due to crossing native/JS code boundaries. And perhaps other browsers have a much faster way of checking for a [[Construct]] call.

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