Function Reference and Execution

In JavaScript, functions can reference and execute

Reference functions: When you assign a function name to a variable, the variable will contain a reference to the function. At this point, the function is not executed immediately, but is referenced. For example: 

function sayHello() {
  console.log("Hello!");
}

const hello = sayHello; // 将 sayHello 函数的引用赋值给 hello 变量

hello(); // 执行 hello 变量，实际上是调用 sayHello 函数

Execute function: When you add parentheses after the function name, the function will be executed immediately, and the result of function execution will be returned. For example: 

 

function addNumbers(num1, num2) {
  return num1 + num2;
}

const sum = addNumbers(5, 7); // 执行 addNumbers 函数，并将执行结果赋值给 sum 变量

console.log(sum); // 将 sum 的值（12）打印到控制台

 

In summary, referencing a function and executing a function are different concepts in JavaScript. In general, a function can be used by referencing it instead of executing it immediately when passed as a variable or when code is executed at a specific point in time (such as an event handler). And when you need to get the execution result of the function, you need to execute the function.