again, you backend-engineers are making something more complicated than needs
be, when simple, throwaway glue-code will suffice. agree with jordan, this
feature is a needless cross-cut of String.prototype.replace.
```
/*jslint
node: true
*/
'use strict';
var dict;
dict = {
'$': '^',
'1': '2',
'<': '<',
'π': 'π',
'-': '_',
']': '@'
};
// output: "testππ_^^[22@ <foo>"
console.log('testππ-$$[11] <foo>'.replace((/[\S\s]/gu), function (character) {
return dict.hasOwnProperty(character)
? dict[character]
: character;
}));
```
kai zhu
[email protected]
> On 19 May 2018, at 4:08 PM, Cyril Auburtin <[email protected]> wrote:
>
> You can also have a
>
> ```js
> var replacer = replacements => {
> const re = new RegExp(replacements.map(([k,_,escaped=k]) =>
> escaped).join('|'), 'gu');
> const replaceMap = new Map(replacements);
> return s => s.replace(re, w => replaceMap.get(w));
> }
> var replace = replacer([['$', '^', String.raw`\$`], ['1', '2'], ['<',
> '<'], ['π', 'π'], ['-', '_'], [']', '@', String.raw`\]`]]);
> replace('testππ-$$[11] <foo>') // "testππ_^^[22@ <foo>"
> ```
> but it's quickly messy to work with escaping
>
> Le sam. 19 mai 2018 Γ 08:17, Isiah Meadows <[email protected]
> <mailto:[email protected]>> a Γ©crit :
> Here's what I'd prefer instead: overload `String.prototype.replace` to
> take non-callable objects, as sugar for this:
>
> ```js
> const old = Function.call.bind(Function.call, String.prototype.replace)
> String.prototype.replace = function (regexp, object) {
> if (object == null && regexp != null && typeof regexp === "object") {
> const re = new RegExp(
> Object.keys(regexp)
> .map(key => `${old(key, /[\\^$*+?.()|[\]{}]/g, '\\$&')}`)
> .join("|")
> )
> return old(this, re, m => object[m])
> } else {
> return old(this, regexp, object)
> }
> }
> ```
>
> This would cover about 99% of my use for something like this, with
> less runtime overhead (that of not needing to check for and
> potentially match multiple regular expressions at runtime) and better
> static analyzability (you only need to check it's an object literal or
> constant frozen object, not that it's argument is the result of the
> built-in `Map` call). It's exceptionally difficult to optimize for
> this unless you know everything's a string, but most cases where I had
> to pass a callback that wasn't super complex looked a lot like this:
>
> ```js
> // What I use:
> function escapeHTML(str) {
> return str.replace(/["'&<>]/g, m => {
> switch (m) {
> case '"': return """
> case "'": return "'"
> case "&": return "&"
> case "<": return "<"
> case ">": return ">"
> default: throw new TypeError("unreachable")
> }
> })
> }
>
> // What it could be
> function escapeHTML(str) {
> return str.replace({
> '"': """,
> "'": "'",
> "&": "&",
> "<": "<",
> ">": ">",
> })
> }
> ```
>
> And yes, this enables optimizations engines couldn't easily produce
> otherwise. In this instance, an engine could find that the object is
> static with only single-character entries, and it could replace the
> call to a fast-path one that relies on a cheap lookup table instead
> (Unicode replacement would be similar, except you'd need an extra
> layer of indirection with astrals to avoid blowing up memory when
> generating these tables):
>
> ```js
> // Original
> function escapeHTML(str) {
> return str.replace({
> '"': """,
> "'": "'",
> "&": "&",
> "<": "<",
> ">": ">",
> })
> }
>
> // Not real JS, but think of it as how an engine might implement this. The
> // implementation of the runtime function `ReplaceWithLookupTable` is omitted
> // for brevity, but you could imagine how it could be implemented, given the
> // pseudo-TS signature:
> //
> // ```ts
> // declare function %ReplaceWithLookupTable(
> // str: string,
> // table: string[]
> // ): string
> // ```
> function escapeHTML(str) {
> static {
> // A zero-initialized array with 2^16 entries (U+0000-U+FFFF), except
> // for the object's members. This takes up to about 70K per instance,
> // but these are *far* more often called than created.
> const _lookup_escapeHTML = %calloc(65536)
>
> _lookup_escapeHTML[34] = """
> _lookup_escapeHTML[38] = "&"
> _lookup_escapeHTML[39] = "'"
> _lookup_escapeHTML[60] = ">"
> _lookup_escapeHTML[62] = "<"
> }
>
> return %ReplaceWithLookupTable(str, _lookup_escapeHTML)
> }
> ```
>
> Likewise, similar, but more restrained, optimizations could be
> performed on objects with multibyte strings, since they can be reduced
> to a simple search trie. (These can be built in even the general case
> if the strings are large enough to merit it - small ropes are pretty
> cheap to create.)
>
> For what it's worth, there's precedent here in Ruby, which has support
> for `Hash`es as `String#gsub` parameters which work similarly.
>
> -----
>
> Isiah Meadows
> [email protected] <mailto:[email protected]>
> www.isiahmeadows.com <http://www.isiahmeadows.com/>
>
>
> On Fri, May 18, 2018 at 1:01 PM, Logan Smyth <[email protected]
> <mailto:[email protected]>> wrote:
> >> It wouldn't necessarily break existing API, since String.prototype.replace
> >> currently accepts only RegExp or strings.
> >
> > Not quite accurate. It accepts anything with a `Symbol.replace` property, or
> > a string.
> >
> > Given that, what you're describing can be implemented as
> > ```
> > Map.prototype[Symbol.replace] = function(str) {
> > for(const [key, value] of this) {
> > str = str.replace(key, value);
> > }
> > return str;
> > };
> > ```
> >
> >> I don't know if the ECMAScript spec mandates preserving a particular order
> >> to a Map's elements.
> >
> > It does, so you're good there.
> >
> >> Detecting collisions between matching regular expressions or strings.
> >
> > I think this would be my primary concern, but no so much ordering as
> > expectations. Like if you did
> > ```
> > "1".replace(new Map([
> > ['1', '2'],
> > ['2', '3],
> > ]);
> > ```
> > is the result `2` or `3`? `3` seems surprising to me, at least in the
> > general sense, because there was no `2` in the original input, but it's also
> > hard to see how you'd spec the behavior to avoid that if general regex
> > replacement is supported.
> >
> > On Fri, May 18, 2018 at 9:47 AM, Alex Vincent <[email protected]
> > <mailto:[email protected]>> wrote:
> >>
> >> Reading [1] in the digests, I think there might actually be an API
> >> improvement that is doable.
> >>
> >> Suppose the String.prototype.replace API allowed passing in a single
> >> argument, a Map instance where the keys were strings or regular expressions
> >> and the values were replacement strings or functions.
> >>
> >> Advantages:
> >> * Shorthand - instead of writing str.replace(a, b).replace(c,
> >> d).replace(e, f)... you get str.replace(regExpMap)
> >> * Reusable - the same regular expression/string map could be used for
> >> several strings (assuming of course the user didn't just abstract the call
> >> into a separate function)
> >> * Modifiable on demand - developers could easily add new regular
> >> expression matches to the map object, or remove them
> >> * It wouldn't necessarily break existing API, since
> >> String.prototype.replace currently accepts only RegExp or strings.
> >>
> >> Disadvantages / reasons not to do it:
> >> * Detecting collisions between matching regular expressions or strings.
> >> If two regular expressions match the same string, or a regular expression
> >> and a search string match, the expected results may vary because a Map's
> >> elements might not be consistently ordered. I don't know if the ECMAScript
> >> spec mandates preserving a particular order to a Map's elements.
> >> - if we preserve the same chaining capability
> >> (str.replace(map1).replace(map2)...), this might not be a big problem.
> >>
> >> The question is, how often do people chain replace calls together?
> >>
> >> * It's not particularly hard to chain several replace calls together.
> >> It's just verbose, which might not be a high enough burden to overcome for
> >> adding API.
> >>
> >> That's my two cents for the day. Thoughts?
> >>
> >> [1] https://esdiscuss.org/topic/adding-map-directly-to-string-prototype
> >> <https://esdiscuss.org/topic/adding-map-directly-to-string-prototype>
> >>
> >> --
> >> "The first step in confirming there is a bug in someone else's work is
> >> confirming there are no bugs in your own."
> >> -- Alexander J. Vincent, June 30, 2001
> >>
> >> _______________________________________________
> >> es-discuss mailing list
> >> [email protected] <mailto:[email protected]>
> >> https://mail.mozilla.org/listinfo/es-discuss
> >> <https://mail.mozilla.org/listinfo/es-discuss>
> >>
> >
> >
> > _______________________________________________
> > es-discuss mailing list
> > [email protected] <mailto:[email protected]>
> > https://mail.mozilla.org/listinfo/es-discuss
> > <https://mail.mozilla.org/listinfo/es-discuss>
> >
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