psi

parse-strings-in-object

Convert string values in JS object to boolean and numbers

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Parse Strings in JS Object

Overview

A very simple module that takes a JavaScript object and returns a new object with string representations of booleans, nulls and numbers converted to their proper types.

So:

  • "true" and "false" becomes true and false
  • "1" and "3.147" become 1 and 3.147
  • "192.168.1.1" is left alone even though it "looks" like a number
  • "null" becomes null

It works recursively, so nested structures are no problem.

Array-like strings (currently, only comma-separated values are intepreted like this), are converted too:

  • "test,one,two,three" becomes ["test","one","two","three"] (an array of strings)
  • "0,1,2,3" becomes [0,1,2,3] (an array of numbers)

Single-element arrays need you to provide a trailing comma to cue the parser appropriately:

  • "1.1," becomes [1.1] (single-element array of numbers)
  • "someString," becomes ["someString"] (single-element array of strings)

This module was originally inspired by the experience of using a configuration module (rc) and having to check things like active === false || active === 'false' repeatedly. I have therefore provided an example of this use case below.

Usage

Install from npm:

npm install parse-strings-in-object

There is only one argument to pass to the module - a valid JavaScript object.

var niceParsedObject = require('parse-strings-in-object')(yourOriginalObject)

Example

const before = {
    active: true,
    anInt: 1,
    aFloat: 1.1,
    justAString: "hello",
    ipAddress: "192.168.1.101"
}

let after = require("parse-strings-in-object")(before);
console.log(JSON.stringify(after, null, 4), typeof after.aFloat, 'and also a', typeof after.anInt);

The output will be:

{
    active: true,
    anInt: 1,
    aFloat: 1.1,
    justAString: "hello",
    ipAddress: "192.168.1.101"
}
number
and also a
number

Notice that both ints and floats are converted correctly to the single "number" type, and a number-like string such as an IP address is left alone (stays a string).

Example in rc config

The rc module for configuration loading allows hard-coded defaults (where types are respected) and also overrides ini files, environment variables and command-line params, where only strings are possible. This makes strict comparisons with === prone to bugs.

The module addresses this nicely. Just wrap the returned config object in a parse-strings-in-object require statement. For example:

const conf = require('parse-strings-in-object')(require('rc')('myapp', {
    anOrdinaryString: "test",
    aBoolean: true,
    aNumber: 9000
}));

Now, if you run your app with --aBoolean=false or --aNumber=9001 then you can safely check whether aBoolean === true or aNumber===9000 and get the expected results.

Why is this necessary?

JavaScript is notoriously loose with typing, so this can get you into trouble. For example, you might get configuration or JSON including strings as values:

"isMaster": "true",
myNumber: "0"

So, now:

console.log(isMaster); // "true": as expected, but actually string
console.log(isMaster==true, isMaster===true); // "false false": oops
console.log(myNumber); // "0": as expected, but actually a string
console.log(typeof myNumber, myNumber==0, myNumber===0); // "string true false": hmmm
console.log(!myNumber); // "true": this is getting confusing

Development and testing

Feel free to improve the module! All pull requests shall be considered.

After npm install you can run unit tests with Mocha like this:

npm run test

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