Do JavaScript functions have return values?

JavaScript functions have return values. If the function contains a return statement, once the return statement is executed, the function will stop running, and the value of the expression after the return will be calculated and returned; if the function does not contain a return statement, undefined will be returned after each statement in the function body is executed. value.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

JavaScript functions have return values.

JavaScript function provides two interfaces to realize interaction with the outside world. The parameters serve as the entrance to receive external information; the return value serves as the exit to feed back the operation results to the outside world.

In the function body, use the return statement to set the return value of the function. Once the return statement is executed, the execution of the function will stop, and the value of the expression following the return will be evaluated and returned. If the function does not contain a return statement, an undefined value will be returned after each statement in the function body is executed.

JavaScript is a weakly typed language, so functions have no type restrictions on the values ​​they receive and output, and JavaScript does not automatically detect the types of input and output values.

Example 1

The following code defines the return value of the function as a function.

function getSum(num1, num2){
    return num1 + num2;
}
var sum1 = getSum(7, 12);      // 函数返回值为：19
var sum2 = getSum(-5, 33);     // 函数返回值为：28

Tip: The return statement is usually defined at the end of the function. When the function reaches the return statement, it will immediately stop running and return to the place where the function was called to continue execution.

Example 2

The parameters of the function are not limited, but the return value can only be one; if you want to output multiple values, you can do it through an array or object design.

function division(dividend, divisor){
    var quotient = dividend / divisor;
    var arr = [dividend, divisor, quotient]
    return arr;
}
var res = division(100, 4)
document.write(res[0]);         // 输出：100
document.write(res[1]);         // 输出：4
document.write(res[2]);         // 输出：25

In the above code, the function return value is an array, which contains 3 elements, thus achieving the purpose of using one return statement to return multiple values.

Example 3

The function body can contain multiple return statements, but only one return statement can be executed. Therefore, the branch structure can be used in the function body to determine the function return value. , or use the return statement to terminate function execution early.

function f(x,y) {
    //如果参数为非数字类型，则终止函数执行
    if (typeof x != "number" || typeof y != "number") return;
    //根据条件返回值
    if (x > y) return x - y;
    if (x < y) return y - x;
    if (x * y <= 0) return x + y;
}

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