Paste Raw JS Code
First thing first. If you're ever stuck learning ReScript, remember that you can always just paste raw JavaScript code into our source file:
%%raw(`/* look ma, regular JavaScript! */var message = "hello";function greet(m) {console.log(m)}`)
// look ma, regular JavaScript!var message = 'hello';function greet(m) {console.log(m);}
The %%raw
special ReScript call takes your code string and pastes it as-is into the output. You've now technically written your first ReScript file!
(The back tick syntax is a multiline string, similar to JavaScript's. Except for us, no escaping is needed inside the string. More on string in a later section.)
While %%raw
lets you embed top-level raw JS code, %raw
lets you embed expression-level JS code:
let add = %raw(`function(a, b) {console.log("hello from raw JavaScript!");return a + b}`)Js.log(add(1, 2))
var add = function(a, b) {console.log('hello from raw JavaScript!');return a + b;};console.log(add(1, 2));
The above code:
- declared a ReScript variable
add
, - with the raw JavaScript value of a function declaration,
- then called that function in ReScript.
If your boss is ever worried that your teammates can't adopt ReScript, just let them keep writing JavaScript inside ReScript files =).
Debugger
You can also drop a %debugger
expression in a body:
let f = (x, y) => {%debuggerx + y}
function f(x, y) {debugger;return (x + y) | 0;}
Output:
function f(x, y) {debugger; // JavaScript developer tools will set an breakpoint and stop herex + y;}
Tips & Tricks
Embedding raw JS snippets isn't the best way to experience ReScript, though it's also highly useful if you're just starting out. As a matter of fact, the first few ReScript projects were converted through:
- pasting raw JS snippets inside a file
- examining the JS output (identical to the old hand-written JS)
- gradually extract a few values and functions and making sure the output still looks OK
At the end, we get a fully safe, converted ReScript file whose JS output is clean enough that we can confidently assert that no new bug has been introduced during the conversion process.
We have a small guide on this iteration here. Feel free to peruse it later.