Install

$ npm install typescript-nullsafe --save

or

$ yarn add typescript-nullsafe

The problem

In JavaScript undefined and nullvalues are hard to check. When using !variablecheck then

• !undefined === true
• !null === true
• !false === true
• !"" === true
• !Number.NaN === true

This basically means

!undefined === !null === !false === !"" == !Number.NaN

which is OK in most cases but when working with data might make code quite messy and end up with the code like:

const parseNumber = (value?: number | null) => {
  if (value === undefined || value === null || Number.isNaN(value)) {
    return "Unknown";
  }
  return `${value}`
}

How would you like to write the same code as:

const parseNumber = (value?: number | null) => 
  hasValue(value) ? `${value}` : "Unknown";

The solution

To reduce the amount of code there are few simple methods described below. Also all methods are typesafe so there should be no problem using method such as:

const method1 = (value: string) => {
/** do something with the string **/
}

const method2 = (value: string | undefined | null) => {
    if (hasValue(value))
        method1(value);
    // or
    if (!hasNoValue(value))
        console.log("no value!");
    else
        method1(value);
}

There should be no TypeScript problems as hasValue enforces the value to be not null nor undefined.

hasValue method

The library solves the typescript issue with having null, undefined, false or empty string introducing methods:

• hasValue(undefined) === false
• hasValue(null) === false
• hasValue(false) === true
• hasValue("") === true
• hasValue(Number.NaN) === false

hasNoValue method

Or reverted

• hasNoValue(undefined) === true
• hasNoValue(null) === true
• hasNoValue(false) === false
• hasNoValue("") === false
• hasNoValue(Number.NaN) === true

valueOf method

And to get default values

• valueOf(undefined, "abc") === "abc"
• valueOf(null, "abc") === "abc"
• valueOf(false, true) === false
• valueOf("", "abc") === ""
• valueOf(Number.NaN, 1) === 1

The second argument can also be a callable and is called when first is undefined, null or Number.Nan for more complex logic

• valueOf(undefined, () => "abc") === "abc"
• valueOf(null, () => "abc") === "abc"
• valueOf(false, () => true) === false
• valueOf("", () => "abc") === ""
• valueOf(Number.NaN, () => 1) === 1

When, let's say we would like to get the default value from some endpoint or asynchronous code then we could use

• valueOfAsync(undefined, async () => "abc") === "abc"
• valueOfAsync(null, async () => "abc") === "abc"
• valueOfAsync(false, async () => true) === false
• valueOfAsync("", async () => "abc") === ""
• valueOfAsync(Number.NaN, async () => 1) === 1

valuesOf method

Or to get value from array

valuesOf([null, 1, undefined, Number.NaN, 2]) === [1,2]

which basically can be written as [null, 1, undefined, Number.NaN, 2].filter(hasValue)but solves the issue with null or undefined:

• valuesOf(null) === []
• valuesOf(undefined) === []

And reduced the amount of code.

valueOfFloat and valueOfInteger methods

Also there is a method valueOfFloat and valueOfInteger which finds numbers from the string as in some regions comma is written as a dot.

• valueOfFloat("ab.0.1") === 0.1

hasNoValueOrEquals

This is helper method to check if both variables are null or undefined or the same. It is shortcut for ((hasNoValue(left) && hasNoValue(right)) || left === right) With one small fix. Sometimes we need to dig deeper so another variable is optionally added to check the value. For example:

hasNoValueOrEquals(
  new Date(),
  new Date(),
  (left, right) => left.getMonth() == right.getMonth()
) === true;

The third argument is called when both first two arguments are not null, undefined nor Number.NaN.

Optional

And introduces implementation of Optional - not so popular but known from other languages for null safeness.