wrap-defaults

wrap-defaults v0.0.1

Generate a function that checks an object for missing properties and fills it with the given default values. The generated function returns the filled object.

Here are some performance comparisons:

• +1000x faster than object spreads in Chrome
• +1000x faster than Object.assign in Chrome
• +150x faster than for...in loop in Chrome

Check out the jsperf to run the tests yourself.

const wrapDefaults = require('wrap-defaults')

const defaults = wrapDefaults({
  a: 1,
  b: 2,
  c: 3,
  d: 4,
})

defaults({
  a: 2,
  d: undefined,
  e: 3,
})

The defaults function above is identical to:

var defaults = {}
function(props) {
  if (props.a === undefined) props.a = defaults.a
  if (props.b === undefined) props.b = defaults.b
  if (props.c === undefined) props.c = defaults.c
  if (props.d === undefined) props.d = defaults.d
}

You can achieve huge performance gains when applying default values in that way. You should avoid using wrapDefaults if it's not much of a hassle to do the inlining on your own.

Custom checks

Provide a function as the 2nd argument for custom value checking.

// Use the default value if property equals null or undefined.
let defaults = wrapDefaults({}, (prop) => prop + ' == null')

// Perform different checks based on property key.
defaults = wrapDefaults({}, (prop, key) => {
  // Avoid checking internal properties.
  if (key[0] == '_') return false
  return `typeof ${prop} == 'undefined'`
})