检查全局变量是否存在的正确方法是什么？

Question

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 1

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 2

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 3

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 4

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 5

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 6

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 7

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 8

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 9

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 10

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === "undefined") {
    var someVar = "hi!";
}

What is the correct way?

Answer 11

If you are not sure whether a global variable is defined, you can always try accessing it and see what happens.

function node_env(name) {
    try {
        return process.env[name];
    } catch (ignore) {}
}