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perf: optimize json string escaping #1717

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perf: optimize json string escaping #1717

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6 changes: 6 additions & 0 deletions lib/tools.js
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,9 @@ function genLog (level, hook) {
}
}

// eslint-disable-next-line
const STR_ESCAPE = /[\u0000-\u001f\u0022\u005c\ud800-\udfff]|[\ud800-\udbff](?![\udc00-\udfff])|(?:[^\ud800-\udbff]|^)[\udc00-\udfff]/

Comment on lines +76 to +78
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I think this is very mysterious (i.e. I have no clue what it is looking for and don't want to expend the mental gymnastics to figure it out). If we are going to introduce complicated regular expressions, I'd rather see https://www.npmjs.com/package/xregexp used to make them legible.

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This contains the groups of chars that should be escaped. Not sure if this can be not mysterious.

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Roughly:

https://runkit.com/embed/rx8essijm0uh

var xregexp = require("xregexp")

const STR_ESCAPE = xregexp(
  `[\u0000-\u001f\u0022\u005c\ud800-\udfff] # chars A - G
  | [\ud800-\udbff] # chars H - J
  (?![\udc00-\udfff]) # BUT NOT something else
  | (?:[^\ud800-\udbff]|^) # some explantation
  [\udc00-\udfff] # something else
  `
  ,
  'x'
)

It's clearer, but could probably be even more clear using XRegExp.build.

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A jsdoc block that explains each part would also suffice (and keep a concerning dependency tree from being added).

// magically escape strings for json
// relying on their charCodeAt
// everything below 32 needs JSON.stringify()
Expand All @@ -84,6 +87,9 @@ function asString (str) {
let found = false
let point = 255
const l = str.length
if (!STR_ESCAPE.test(str)) {
return '"' + str + '"'
}
if (l > 100) {
return JSON.stringify(str)
}
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