Duplicate Function Signature and Variable in JavaScript

function_signature.js

// SyntaxError: foo has alreay been declared
const foo = (a, b) => {
    console.log(a, b);
};

const foo = (a) => {
    console.log(a);
};

foo(10, 100);
foo(200);

// No Error Throw, second one overwrite first one
// output: 10

function bar(a, b) {
    console.log(a, b);
}

function bar(a) {
    console.log(a);
}

bar(10, 100);