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@thi.ng/resolve-map

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Readme

@thi.ng/resolve-map

This project is part of the @thi.ng/umbrella monorepo.

About

DAG resolution of vanilla objects & arrays with internally linked values.

It's common practice to use nested JS objects for configuration purposes. Frequently some values in the object are copies or derivatives of other values, which can lead to mistakes during refactoring and / or duplication of effort.

To avoid these issues, this library provides the ability to define single sources of truth, create references (links) to these values and a provide a resolution mechanism to recursively expand their real values and / or compute derived values. Both absolute & relative references are supported.

API

`resolveMap(obj)`

Visits all key-value pairs in depth-first order for given object or array, expands any reference values, mutates the original object and returns it. Cyclic references are not allowed or checked for and if present will cause a stack overflow error. However, refs pointing to other refs are recursively resolved (again, provided there are no cycles).

Reference values are special strings representing lookup paths of other values in the object and are prefixed with -> for relative refs or ->/ for absolute refs. Relative refs are resolved from currently visited object and support "../" prefixes to access parent levels. Absolute refs are always resolved from the root level (the original object passed to this function).

resolveMap({a: 1, b: {c: "->d", d: "->/a"} })
// { a: 1, b: { c: 1, d: 1 } }

If a value is a function, it is called with a single arg resolve, a function which accepts a path (without -> prefix) to look up other values. The return value of the user provided function is used as final value for that key. This mechanism can be used to compute derived values of other values stored in the object. Function values will always be called only once. Therefore, in order to associate a function as value to a key, it needs to be wrapped with an additional function, as shown for the e key in the example below.

// `a` is derived from 1st array element in `b.d`
// `b.c` is looked up from `b.d[0]`
// `b.d[1]` is derived from calling `e(2)`
// `e` is a wrapped function
res = resolveMap({
  a: (resolve) => resolve("b.c") * 100,
  b: { c: "->d.0", d: [2, (resolve) => resolve("../../e")(2) ] },
  e: () => (x) => x * 10,
})
// { a: 200, b: { c: 2, d: [ 2, 20 ] }, e: [Function] }

res.e(2);
// 20

Installation

yarn add @thi.ng/resolve-map

Usage examples

import { resolveMap } from "@thi.ng/resolve-map";

resolveMap({
    colors: {
        bg: "white",
        text: "black",
        selected: "red",
    },
    main: {
        fontsizes: [12, 16, 20]
    },
    button: {
        bg: "->/colors.text",
        label: "->/colors.bg",
        // resolve with abs path inside fn
        fontsize: (resolve) => `${resolve("/main.fontsizes.0")}px`,
    },
    buttonPrimary: {
        bg: "->/colors.selected",
        label: "->/button.label",
        // resolve with relative path inside fn
        fontsize: (resolve) => `${resolve("../main.fontsizes.2")}px`,
    }
})
// {
//     colors: {
//         bg: "white",
//         text: "black",
//         selected: "red"
//     },
//     main: {
//         fontsizes: [ 12, 16, 20 ]
//     },
//     button: {
//         "bg": "black",
//         "label": "white",
//         "fontsize": "12px"
//     },
//     buttonPrimary: {
//         bg: "red",
//         label: "black",
//         fontsize: "20px"
//     }
// }

Authors

Karsten Schmidt