elv

Elvis operator functionality for JavaScript.

With the absence of an Elvis (existential) operator in JavaScript, I often find myself writing the same checks to see if something is undefined over and over and over again. The || operator in JavaScript is generally inadequate for this purpose, because it fails to account for Booleans. So, I decided to create a small module to clean up the redundant code.

API

elv(val)

Determines whether or not the argument val is defined. Returns false if val is undefined or null, or will otherwise returns true.

Parameters

• val: (required) the value on which to perform an existential check.

Example:

const elv = require('elv');
 
const foo = { foo: 'bar' };
console.log(elv(foo)); // true
 
const bar = undefined;
console.log(elv(bar)); // false
 
const baz = false;
console.log(elv(baz)); // true
 
const qux = null;
console.log(elv(qux)); // false

elv.behavior.enableFalse

Gets or sets whether or not existential checks should check if value is not false. Defaults to false (not enabled).

Example:

const elv = require('elv');
 
console.log(elv(false)); // true
 
elv.behavior.enableFalse = true;
 
console.log(elv(false)); // false

elv.behavior.enableNaN

Gets or sets whether or not existential checks should check if value is not Number.NaN. Defaults to false (not enabled).

Example:

const elv = require('elv');
 
console.log(elv(Number.NaN)); // true
 
elv.behavior.enableNaN = true;
 
console.log(elv(Number.NaN)); // false

elv.behavior.enableNull

Gets or sets whether or not existential checks should check if value is not null. Defaults to true (enabled).

Example:

const elv = require('elv');
 
console.log(elv(null)); // false
 
elv.behavior.enableNull = false;
 
console.log(elv(null)); // true

elv.behavior.enableUndefined

Gets or sets whether or not existential checks should check if value is not undefined. Defaults to true (enabled).

Example:

const elv = require('elv');
 
console.log(elv(undefined)); // false
 
elv.behavior.enableUndefined = false;
 
console.log(elv(undefined)); // true

elv.coalesce(...val)

Accepts a series of parameters, and returns the first argument that is defined.

Parameters

• ...val: (required) the values to coalesce.

Example:

const elv = require('elv');
const coalesce = elv.coalesce;
 
const foo = undefined;
const bar = null;
const baz = 'hello world';
const qux = true;
 
const result = coalesce(foo, bar, baz, qux);
console.log(result); // hello world

Deferred Function Execution

If the final argument passed to elv.coalesce() is reached, and it is a function, then it will evaluate that function and return its result. The idea is to ensure that potentially expensive functions to execute are not run unless absolutely necessary.

Example

const elv = require('elv');
const coalesce = elv.coalesce;
 
const getFoo = function() {
  // do something expensive to compute theValueOfFoo
  return theValueOfFoo;
};
 
class Bar {
  constructor(foo) {
    // the getFoo function will only be executed if foo is not truthy
    this._foo = coalesce(foo, getFoo);
  }
}

elv.ncoalesce(...val)

Accepts a series of parameters, and returns the first argument that is defined. Works just like elv.coalesce(), but it does not lazily execute functions.

Parameters

• ...val: (required) the values to coalesce.

Example:

const elv = require('elv');
const coalesce = elv.coalesce;
 
const foo = undefined;
const bar = null;
const baz = 'hello world';
const qux = true;
 
const result = coalesce(foo, bar, baz, qux);
console.log(result); // hello world

elv.populated(val)

In addition to performing an existential check, determines if a given string, array or object is not empty. An empty object is one that has no properties.

Parameters

• val: (required) the value on which to perform an existential and populated check.

Examples:

const elv = require('elv');
 
console.log(elv.populated('foo')); //true
console.log(elv.populated(['foo', 'bar'])); //true
console.log(elv.populated({ foo: 'bar' })); //true
console.log(elv.populated(null)); // false
console.log(elv.populated('')); // false
console.log(elv.populated([])); // false
console.log(elv.populated({})); // false

elv.tryGet(val, index [, default])

Attempts to get an entry from an array at the given index. If the given index is out of the array's bounds, then a given default value is returned.

Parameters

• val: (required) the array from which an entry is being fetched.

• index: (required) the index being referenced in the array.

• default: (optional) the default value if index is not found.

Examples

const elv = require('elv');
 
const val = ['foo', 'bar', 'baz', 'qux'];
 
console.log(elv.tryGet(val, 5)); // undefined
console.log(elv.tryGet(val, 5, 42)); // 42
console.log(elv.tryGet(val, 2)); // baz