Function
objects created with the Function
constructor are parsed when the function is created. This is less efficient than creating a function with a function expression or function declaration and calling it within your code, because such functions are parsed with the rest of the code.
All arguments passed to the function, except the last, are treated as the names of the identifiers of the parameters in the function to be created, in the order in which they are passed. The function will be dynamically compiled as a function expression, with the source assembled in the following fashion:
`function anonymous(${args.join(",")}
) {
${functionBody}
}`;
This is observable by calling the function's toString()
method.
However, unlike normal function expressions, the name anonymous
is not added to the functionBody
's scope, since functionBody
only has access the global scope. If functionBody
is not in strict mode (the body itself needs to have the "use strict"
directive since it doesn't inherit the strictness from the context), you may use arguments.callee
to refer to the function itself. Alternatively, you can define the recursive part as an inner function:
const recursiveFn = new Function(
"count",
`
(function recursiveFn(count) {
if (count < 0) {
return;
}
console.log(count);
recursiveFn(count - 1);
})(count);
`,
);
Note that the two dynamic parts of the assembled source — the parameters list args.join(",")
and functionBody
— will first be parsed separately to ensure they are each syntactically valid. This prevents injection-like attempts.
new Function("/*", "*/) {");