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@thi.ng/dynvar

dynvar

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

About

Dynamically scoped variable bindings.

References:

Status

ALPHA - bleeding edge / work-in-progress

Installation

yarn add @thi.ng/dynvar
// ES module
<script type="module" src="https://unpkg.com/@thi.ng/dynvar?module" crossorigin></script>

// UMD
<script src="https://unpkg.com/@thi.ng/dynvar/lib/index.umd.js" crossorigin></script>

Package sizes (gzipped, pre-treeshake): ESM: 300 bytes / CJS: 354 bytes / UMD: 439 bytes

Dependencies

API

Generated API docs

TODO - See tests for usage...

Logging example

import { dynvar } from "@thi.ng/dynvar";
import { appendFileSync } from "fs";

interface Logger {
    log(...args: any[]): void;
}

// create dynamically scoped variable
// set default/root binding
const logger = dynvar<Logger>(console);

// dummy function using `logger`
const foo = () => {
    // deref() returns var's current value
    logger.deref().log("begin foo...");
    for (let i = 0; i < 5; i++) {
        logger.deref().log(i);
    }
    logger.deref().log("foo done.");
};

foo();
// (output in console)
// begin foo...
// 0
// 1
// 2
// 3
// 4
// foo done.

// Alternative Logger impl
class FileLogger implements Logger {
    constructor(protected path: string) {}

    log(...args: any[]) {
        appendFileSync(this.path, args.join(", ") + "\n");
    }
}

// re-execute `foo` with temporary dynamic scope in which
// logger is bound to given new value (i.e. here file logger)
logger.withBinding(new FileLogger("./foo.txt"), foo);

// old scope again (back to using console)
logger.deref().log("good bye");
// "good bye"

Display log file contents:

cat foo.txt
# begin foo...
# 0
# 1
# 2
# 3
# 4
# foo done.

Authors

Karsten Schmidt

License

© 2016 - 2020 Karsten Schmidt // Apache Software License 2.0

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