koalaesce

About

A simple null-coalescing library for JS, providing behavior much like C#'s ?? operator or Groovy's ?. operator.

koalaesce.get allows you to pass a base object and chain of property names and retrieve the last link in the chain, without worrying about the intermediate null checks. It also features invocation of functions found along the way, and the ability to specify a default value if the chain could not be resolved.

Usage

koalaesce is set up as a utility class, so you should start by requiring it:

let koalaesce = require("koalaesce");

The gulpfile included with koalaesce builds UMD modules, so koalaesce should be with most module systems and is usable within the browser as well as node/io tools.

Two primary methods are exposed from this class: get and getOrDefault. For users preferring exceptions over null, the getOrThrow method is provided. All use the same underlying implementation.

get

koalaesce.get works down through a chain, returning the last link (if it can be found). If a link is missing or a null link is encountered before the end of the chain, it will return null. For example:

let obj = {foo: {bar: 3}};
koalaesce.get(obj, "foo", "bar") === 3;

let obj = {foo: null};
koalaesce.get(obj, "foo", "bar") === null; // null since foo is null, but we still need bar

let obj = {foo: {baz: 3}};
koalaesce.get(obj, "foo", "bar") === null; // null since foo does not have a bar, only baz

To invoke a function encountered along the chain, the function name (and any arguments) should be provided as an array:

let obj = {foo: (a) => { return a+1; }};
koalaesce.get(obj, ["foo", 2]) === 3;

Normal links must not be provided as an array, koalaesce uses arrays to detect when it should attempt to invoke a link.

getOrDefault

koalaesce.getOrDefault behaves almost identically to koalaesce.get, but allows you to specify a default value to be returned rather than null:

let obj = {foo: null};
koalaesce.getOrDefault(obj, 3, "foo", "bar") === 3;

let obj = {foo: {baz: 3}};
koalaesce.getOrDefault(obj, 4, "foo", "bar") === 4;

getOrThrow

koalaesce.getOrThrow will throw an exception rather than returning null if a missing or null link is encountered:

let obj = {foo: null};
try {
    koalaesce.get(obj, "foo", "bar");
} catch (e) {
    e.constructor === NullLinkError;
}

let obj = {foo: {baz: 3}};
try {
    koalaesce.get(obj, "foo", "bar");
} catch (e) {
    e.constructor === MissingLinkError;
}

This can be useful in environments where an exception may trigger other behavior, or if a stacktrace is desired. The link where the error was encountered will be included in the error message.

getNamed

koalaesce.getNamed behaves much like koalaesce.get, but only takes two arguments: the base object and a string of all links in the chain, separated by .s. This is stylistically similar to using the obj.foo.bar syntax, with the additional checks koalaesce provides.

let obj = {foo: {bar: 3}};
koalaesce.getNamed(obj, "foo.bar") === 3;

Note: This does not support property names containing the '.' character, yet. Support for those is planned.

getNamedOrDefault

koalaesce.getNamedOrDefault behaves much like koalaesce.getOrDefault, but only takes three arguments: the base object, a default return value, and a string of links in the chain. It uses the same '.'-separated behavior as getNamed:

let obj = {foo: {baz: 3}};
koalaesce.getNamedOrDefault(obj, 4, "foo.bar") === 4;

Note: The same caveat about property names containing the '.' character applies to getNamedOrDefault as to getNamed.