使用 Function() 构造函数作为闭包

Question

I'm trying to do something like this:

function simpleOperations(operation) {
    let myFanction = new Function('a', 'b', 'a ' + operation + ' b');
    return myFanction
}

let sum = simpleOperations("+")
let multiplicate = simpleOperations("*")

console.log("your sum is: " + sum(3,7));
console.log("your product is: " + multiplicate(3,7));

and instead of getting:

your sum is: 10
your product is: 21

I'm getting this:

your sum is: undefined
your product is: undefined

Do you have any thoughts on how to fix it? :)

Answer 1

The text body of the function needs to return the value, otherwise your a + b or a * b etc will just be an unused expression.

 function simpleOperations(operation) { let myFanction = new Function('a', 'b', 'return a ' + operation + ' b'); return myFanction } let sum = simpleOperations("+") let multiplicate = simpleOperations("*") console.log("your sum is: " + sum(3,7)); console.log("your product is: " + multiplicate(3,7));

Answer 2

Using Function is an anti-pattern. It's one degree away from eval and there's always a better way to write things, especially considering JavaScript already supports first-class functions -

 const add = (a, b) => a + b const multiply = (a, b) => a * b console.log("your sum is: " + add(3,7)) console.log("your product is: " + multiply(3,7))

your sum is: 10
your product is: 21

If instead you want to access functions using "+" and "*" strings, you can create a simple lookup and throw an Error when a particular operation is not supported -

 const operations = { "+": (a, b) => a + b, "*": (a, b) => a * b } function simpleOperations(op) { const f = operations[op] if (f == null) throw Error(`unsupported operation: ${op}`) return f } const add = simpleOperations("+") const multiply = simpleOperations("*") console.log("your sum is: " + add(3,7)) console.log("your product is: " + multiply(3,7)) const divide = simpleOperations("/") // <- not yet implemented

your sum is: 10
your product is: 21
Error: unsupported operation: /

Implementing a simple calculator is a great way to learn how to write your first programming language. If this sort of thing interests you, see this related Q&A .