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86 lines
2.1 KiB
86 lines
2.1 KiB
/*===
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args: 1 2 3 4
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this: [object global]
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args: f2 1 2 3
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this: this-f2
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args: f2 f3 1 2
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this: this-f2
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===*/
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function orig(x,y,z,w) {
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print('args:', x, y, z, w);
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print('this:', this);
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}
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var f1, f2, f3, f4;
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f1 = orig;
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f2 = f1.bind('this-f2', 'f2');
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f3 = f2.bind('this-f3', 'f3');
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/* Plain function call, 'this' binding will be the global object. */
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f1(1, 2, 3, 4);
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/* Bound function: bind 'this' to 'this-f2' and prepend 'f1' to argument list:
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*
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* f2(1, 2, 3)
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* --> f1('f2', 1, 2, 3) this='this-f2'
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*/
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f2(1, 2, 3);
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/* Second order bound function: note the behavior of the this binding:
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*
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* f3(1, 2)
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* --> f2('f3', 1, 2) this='this-f3'
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* --> f1('f2', 'f3', 1, 2) this='this-f2'
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*
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* In other words:
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*
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* - The effective 'this' binding comes from the bound function right before
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* the actual non-bound function (not the outermost bound function).
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*
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* - The argument list to be prepended (for the final non-bound function call)
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* can be formed by concatenating the [[BoundArgs]] lists of the bound
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* functions, from innermost to outermost. Or alternatively, by starting
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* with an empty list, process each bound function from outermost to innermost,
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* prepending the [[BoundArgs]].
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*/
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f3(1, 2);
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/*===
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args: 1 2 3 4
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this: this-f2
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args: 1 2 3 4
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this: this-f2
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===*/
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/* Example of [[BoundArgs]] concatenation:
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*
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* f1 <-- f2, [[BoundArgs]] = [1,2] <-- f3, [[BoundArgs]] = [3,4]
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*
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* Process from outermost to innermost, prepending [[BoundArgs]]
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*
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* []
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* [3,4] + [] = [3,4] (process f3)
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* [1,2] + [3,4] = [1,2,3,4] (process f2)
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* [1,2,3,4] (f1 is not bound, finish)
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*
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* The ultimately effective [[BoundThis]] is the one right before the non-bound
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* function, i.e. f2's [[BoundThis]] here.
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*
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* For a "collapsed" bound function:
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*
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* [[BoundArgs]] = [1,2,3,4]
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* [[BoundThis]] = 'this-f2'
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* [[TargetFunction]] = f1
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*/
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f1 = orig;
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f2 = f1.bind('this-f2', 1, 2);
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f3 = f2.bind('this-f3', 3, 4);
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f4 = f1.bind('this-f2', 1, 2, 3, 4); // equivalent to f3
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f3();
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f4();
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