Parse, Don't Validate (2019)

In typescript parsing/asserting types with combinators works very well merging runtime with static type system [0], it has to be used at i/o boundary, then it enters static type system guarantee and no assertions are necessary, makes very nice codebase.

[0] https://github.com/appliedblockchain/assert-combinators

I wish it had actual proper examples. I've no idea how to use that.

from a look at the readme, you combine those `$.TYPE` things to build a validation function that checks if its argument matches some pattern (and throws an exception if it doesn't).

  import * as $ from '@appliedblockchain/assert-combinators'

  const validateFooBar = (
    $.object({
      foo: $.string,
      bar: $.boolean
    })
  )
  // probably roughly equivalent to
  /*
  const validateFooBar = (x) => {
    console.assert(
      typeof x === 'object' &&
      typeof x.foo === 'string' &&
      typeof x.bar === 'boolean'
    )
    return x
  }
  */


  const test1 = { foo: "abc", bar: false }
  const test2 = { foo: 0, quux: true } 
  const { foo, bar } = validateFooBar(test1) // ok
  const oops = validateFooBar(test2) // throws error

the source is pretty readable too if you want to get an idea how it works.

https://github.com/appliedblockchain/assert-combinators/blob...

https://github.com/appliedblockchain/assert-combinators/blob...