String-replace-async NPM

string-replace-async

A vesion of "string".replace() that knows how to wait

Installation

$ npm install string-replace-async

Note: If you're using pre-14 version of Node or your node codebase isn't converted to ES Modules yet, please use Version 2 specifically!

$ npm install string-replace-async@^2.0.0

Usage

import replaceAsync from "string-replace-async";

await replaceAsync("#rebeccapurple", /#(\w+)/g, async (match, name) => {
  let color = await getColorByName(name);
  return "#" + color + " (" + name + ")";
});

The Why

Say you have a task of replacing color names with their respective hex codes.

let spec = "I want background to be #papayawhip and borders #rebeccapurple.";
// make it "I want background to be #FFEFD5 (papayawhip) and borders #663399 (rebeccapurple).";

Luckily, strings in JavaScript have this handy replace method built in, so you use it.

spec.replace(/#(\w+)/g, (match, name) => {
  let color = getColorByName(name);
  return "#" + color + " (" + name + ")";
});

Time passes, a new requirement emerges: now you have to query a database for custom colors. This is an async operation, so naturally you convert getColorByName into async function.

Turns out it has a cost: now all the code above should also be async. You try this:

await spec.replace(/#(\w+)/g, async (match, name) => {
  let color = await getColorByName(name);
  return "#" + color + " (" + name + ")";
});

Unfortunately, this code doesn't work as you expect. Built in menthod wasn't designed to work as async function.

This is where string-replace-async comes in:

await replaceAsync(spec, /#(\w+)/g, async (match, name) => {
  let color = await getColorByName(name);
  return "#" + color + " (" + name + ")";
});

Yay!

string-replace-async is nothing but direct String.prototype.replace replacement that awaits your function and returns a Promise for results.

API

API is String.prototype.replace(), except the first argument is a string itself.

replaceAsync(string, searchValue, replace)

Runs replace and waits for it to resolve before replacing searchValue with results. If searchValue is a global RegExp, replace will be called concurrently for every match.

string

Type: string
Required

An input string.

searchValue

Type: regexp, string

An expression to match substrings to replace.

replace

Type: function, string

A function that takes several arguments and returns a promise. Resolved value will be used as replacement substring.

A Note on Concurrency

Previously this module had an additional function seq() that ran replace functions one by one instead of all at once. We decided to remove it to narrow our scope. Here's a snippet that achieves the same effect:

let sequence = Promise.resolve();
let seq = (fn) => (...args) => (sequence = sequence.then(() => fn(...args)));

await replaceAsync(
  "#rebeccapurple, #papayawhip",
  /#(\w+)/g,
  seq(async (match, name) => {
    let color = await getColorByName(name);
    return "#" + color + " (" + name + ")";
  })
);