你好：“世界”为什么这是有效的JavaScript？

Question

I was messing around in console when I typed in echo : "test" and to my suprised the string "test" was returned to console.

How come this is valid syntax without a ? in a (boolean) ? trueresult : falseresult (boolean) ? trueresult : falseresult

Are there possible uses except a fancy way to mess in console?

Answer 1

In this case echo: is creating a label.

See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label

Answer 2

The echo: is creating the label and hence the output

Description

You can use a label to identify a loop, and then use the break or continue statements to indicate whether a program should interrupt the loop or continue its execution.

Note that JavaScript has NO goto statement, you can only use labels with break or continue.