Note that you need not do anything special to create a bound function for use with new. bind ( null, 0 /*x*/ ) const axisPoint = new YAxisPoint ( 5 ) ĪxisPoint instanceof YAxisPoint // true new YAxisPoint ( 17, 42 ) instanceof Point // true toString ( ) // '1,2' // The thisArg's value doesn't matter because it's ignored const YAxisPoint = Point. The arguments that fn ultimately receives are, in order: the arguments bound by boundFn, arguments bound by boundFn2, and the arguments received by boundFn2.įunction Point ( x, y ) const p = new Point ( 1, 2 ) When boundFn2 is called, it would call boundFn, which in turn calls fn. The newly bound thisArg value is ignored, because the target function of boundFn2, which is boundFn, already has a bound this. restArgs) for the effect when it's called (but not when boundFn is constructed).Ī bound function can be further bound by calling boundFn.bind(thisArg, /* more args */), which creates another bound function boundFn2.

You can generally see const boundFn = fn.bind(thisArg, arg1, arg2) as being equivalent to const boundFn = (.restArgs) => fn.call(thisArg, arg1, arg2. These values are stored in advance, instead of being passed at call time. The bound function will store the parameters passed - which include the value of this and the first few arguments - as its internal state. Calling the bound function generally results in the execution of the function it wraps, which is also called the target function. The bind() function creates a new bound function.

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