使用在函数外部声明的变量的Javascript会返回值+未定义

Question

var name = "myName";

function test() {
    document.write(name);
}

var testcheck= test();

document.write(testcheck);

This returns " myNameundefiend " that is the value+undefined why is that happening ?

Answer 1

You're not returning a value from your test function, making the testcheck variable undefined .

The test() call first writes the name to the document, then document.write(testcheck); adds undefined behind that.

You'll need to return name from the function:

function test() {
    document.write(name);
    return name;
}

There's no need to document.write twice. Either only keep it in the function, or remove it from the function and use document.write(testcheck); .