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72 lines
1.8 KiB
Markdown
72 lines
1.8 KiB
Markdown
## Name
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js - evaluate JavaScript
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## Synopsis
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```**sh
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$ js [options...] [script.js]
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```
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## Description
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`js` evaluates JavaScript programs using the LibJS engine. If you pass it a path
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to a script file, it will execute that script. Otherwise, it enters the
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Read-Eval-Print-Loop (REPL) mode, where it interactively reads pieces (usually,
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single lines) of code from standard input, evaluates them in one shared
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interpreter context, and prints back their results. This mode is useful for
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quickly experimenting with LibJS.
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Run `help()` in REPL mode to see its available built-in functions.
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## Options
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* `-A`, `--dump-ast`: Dump the Abstract Syntax Tree after parsing the program.
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* `-l`, `--print-last-result`: Print the result of the last statement executed.
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* `-g`, `--gc-on-every-allocation`: Run garbage collection on every allocation.
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* `-s`, `--no-syntax-highlight`: Disable live syntax highlighting in the REPL
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* `-t`, `--test-mode`: Run the interpreter with added functionality for the test harness
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## Examples
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Here's how you execute a script:
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```sh
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$ js ~/js/type-play.js
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```
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And here's an example of an interactive REPL session:
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```js
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$ js
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> function log_sum(a, b) {
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> console.log(a + b)
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> }
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undefined
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> log_sum(35, 42)
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77
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undefined
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```
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## Test mode
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In test mode, the `load()` function is added to the global object and can be used
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to load further test utility functions defined in `LibJS/Tests/test-common.js`.
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Typically a test will look like this:
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```js
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load("test-common.js");
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try {
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// test feature
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console.log("PASS");
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} catch (e) {
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console.log("FAIL: " + e);
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}
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```
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Available functions in `test-common.js`:
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* `assert(expression)`: Throws an `AssertionError` if condition does not evaluate to a truthy value
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* `assertNotReached()`: Throws an `AssertionError`, use to ensure certain code paths are never reached
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