Unable to identify IIFE.

[vikrant-sahu]

I have the following snippet which the tree-sitter is unable to recognise:

(function () {
var userName = "Steve";

function display(name)
{
alert("MyScript2.js: " + name);
}

display(userName);
})();

It just skips this part of the code.

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[patrickt]

Can you be more specific about what you’ve tried, and in what circumstances your code is skipped? I pasted the above code into the tree-sitter playground and it parsed correctly.

[vikrant-sahu]

Okay. Sorry I have to put the code above it to reproduce it.

function add(x,y){
    return x+y
}

var subtract = function(x,y){
    return x-y
}

(function () {
var userName = "Steve";

function display(name)
{
alert("MyScript2.js: " + name);
}

display(userName);
})();

The above code should has 3 blocks i.e a function declaration, a variable declaration(actually a function) and a IIFE. It's not considering the IIFE as separate block and embedding it inside the previous block i.e variable declaration.

[patrickt]

Aha, yeah, that looks problematic—without a semicolon there, it tries to parse that (function ()) as arguments to a hypothetical function call that would be returned from the above function() call. Inserting a semicolon after the subtract function body appears to avoid this, but (assuming that the above passes correctly in a JS engine) we should fix this. Unfortunately, I know very little about the JS/TS grammar, so I’ll defer to @maxbrunsfeld.

[maxbrunsfeld]

I think that’s the correct parse, and you’d need to put a semicolon at the end of your var declaration, but I might be wrong.

I’m on mobile. Could someone double check the behavior of that code using node or a browser?

[patrickt]

Looks like node accepts it without the semicolon. After a function alert(str) { console.log(str) } in the node console, it prints MyScript2.js: Steve.

[vikrant-sahu]

yeah, that's common in JS. The thing is JS is very dynamic.

Also when a function or a class starts with export or const it calls it export_statement and lexical_declaration irrespective of if it's function or a class.

[maxbrunsfeld]

Tree-sitter-javascript's parse tree is correct.

@vikrant-sahu JavaScript's automatic semicolon insertion rules can be a bit tricky. The behavior can be especially confusing when you begin a line with ( or [, because if you don't use semicolons, that [ or ( will almost always be treated as a continuation of the previous statement.

The most common practice is to either:

1. use semicolons at the end of statements, or
2. when beginning a line with ( or [, add a semicolon at the beginning of that line.

In the future though, before opening issues like this, first double check that your understanding of the code is correct by running it. In this case, notice how the behavior of the code changes if you add a semicolon at the end of the var statement.