> -----Original Message----- > From: [email protected] [mailto:es-discuss- > [email protected]] On Behalf Of Angus Croll > Sent: Saturday, April 21, 2012 16:03 > To: Allen Wirfs-Brock > Cc: es-discuss > Subject: Re: A few arrow function specification issues > > >>4) Should it be a dynamic error to try to use apply/call to set the > this binding of an arrow function. > > >>Cons > >>To much existing code speculatively binding the this value when > invoking a function. > > >>I propose that call/apply simply ignore the this value when invoked on > an arrow function. > > What is the pro of ignoring explicit |this| binding instructions in > call/apply on arrow functions? > What is the con of continuing to allow legacy code to speculatively bind > the |this| value when invoking any function? > Why is it so important that fat arrows do a hard |this| binding?
It's important, as someone who hands off an arrow function to another part of the system, to ensure that `this` means what it meant while I was originally writing the code. This guarantee is vital for predictability of behavior. Consider let mapped = array.map((el) => el * this.x) If I cannot guarantee a lexical `this`, I am back to programming with `let that = this`, which is part of what arrow functions are trying to avoid. The only alternative is reading the source code and/or spec for every system that I hand off an arrow function to, since I need to know if they will clobber the lexical `this` I was trying to program against. Note that this isn't a security issue---I'm not worried about "malicious code" messing me up. I'm simply trying to juggle the minimum number of factors on my precious brainstack, and when I'm trying to get a mapped array, I really don't want to think about whether `map` is going to mess with my `this`. _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
