问题
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- Usage of the backtick character (`) in JavaScript? 7 answers
I am to trying to learn Express library and Node.js one step at a time. First I am looking at is the specifics of the Node reqiure(moduleName) function.
I took a look at the documentation for this, and found some weird code in the example documentation:
const circle = require(\'./circle.js\');
console.log( `The area of a circle of radius 4 is ${circle.area(4)}`);
More specifically the ${circle.area(4)} bit.
From what I understand the $ in JavaScript is just like any other variable. When we are using it on client side web development it is used as a delegate for the document function (I think). What is it assigned to when using node?
On top of that, what does this syntax mean? ${circle.area(4)}
If $ is just a reference to some function someFunction(), wouldn\'t it be equivalent to this someFunction(){cirle.area(4)}. I am not seeing how that could be valid syntax.
Also, why wouldn\'t they just directly call the circle.area() function directly anyways?
回答1:
This:
`The area of a circle of radius 4 is ${circle.area(4)}`
is an example of ES2015 template strings.
It interpolates whatever circle.area(4) represents directly into the string. If you're curious about this or other ES2015 features, I recommend checking out Babel and playing around in the REPL.
Here's a very simple example to get you started.
You can see this ES2015 code:
const foo = 'some text';
console.log(`${foo} is interpolated.`);
is transpiled to its ES5 equivalent - a simple + concatenation:
var foo = 'some text';
console.log(foo + ' is interpolated.');
来源：https://stackoverflow.com/questions/36107981/what-does-this-code-in-the-node-docs-mean