how to get the word below the cursor when hovering over in LSP?

Question

I am making a vscode extension for a programming language. At first i was doing all of the work using the extension api. Now i want to switch LSP. The feature I had implemented was that show the definition of builtin functions on hover.

This was the code:

vscode.languages.registerHoverProvider("lc", {
        provideHover(document, position) {
            const word = document.getText(
                document.getWordRangeAtPosition(position, /\b\w+(?=\(.*\))/)
            );
            if (builtin_funcs[word] != undefined) {
                return new vscode.Hover(
                    new vscode.MarkdownString(`${builtin_funcs[word]}`)
                );
            } else {
                return null;
            }
        },
    });

i was using the getWordRangeAtPosition function with the regex /\b\w+(?=\(.*\))/ to match functions. After getting the function name i searched it in the builtin_funcs array and returned the definition.

Now i want to port this to LSP but i can't find getWordRangeAtPosition function equivalent.