•js — JavaScript functions

•js source returns a BPL function that calls the JavaScript function source evaluates to. f Y calls it with Y, and X f Y with X then Y. For example, after h←•js "Math.hypot", 3 h 4 is 5. Only the browser build has •js. A page that runs BPL can also give it JavaScript functions and values by name, with Session.bind.

Arguments cross into JavaScript, and results come back, as this table shows. •canvas, Session.eval and Session.bind follow it too.

BPL	JavaScript
Number	Number. A Boolean is true or false.
String	String
Record	Object
Array of numbers	{shape, data}. data is a Float64Array for approximate and fractional numbers. For integers, it’s a Uint8Array, Int16Array, Int32Array or BigInt64Array, at the width BPL stores them. Complex numbers are their real and imaginary parts in turn, with a last axis of length 2.
Any other array	{shape, data}, with data an Array of items

An array with axis names or keys also has axis_names or axis_keys. A function or operator can’t cross into JavaScript. Coming back, a JavaScript number becomes an approximate number, and a BigInt an exact one. An Array becomes a vector. An object with shape and data becomes an array, and any other object a record. A JavaScript function becomes a BPL function. undefined and null give no result.

Errors: DOMAIN for source that doesn’t give a function, an exception thrown by the JavaScript, or a value that can’t cross.