Hướng dẫn dùng read-from-string JavaScript
Nội dung bài viết JavaScript string methods giúp lập trình viên có thể thao tác với Làm việc với String luôn luôn là nhiều, rất nhiều. Mỗi ngày tỷ lệ làm việc với Ví dụ: Sử dụng Ví dụ: Thậm chí bạn cũng thể thử với text sau: Với Nếu như bạn đang loay hoay tìm cách Convert String to Array thì đây là thứ bạn cần. Sử dụng Cuối cùng đó là việc sử
dụng Vậy thôi, nhìn đơn giản thôi, nhưng mỗi lần sử dụng lại đi tìm trên Google đấy. Đảm bảo. Next,
we'll turn our attention to strings — this is what pieces of text are called in programming. In this article, we'll look at all the common things that you really ought to know about strings when learning JavaScript, such as creating strings, escaping quotes in strings, and joining strings together. Words are very important to humans — they are a large part of how we communicate. Since the Web is a largely text-based medium designed to allow humans to communicate and share information, it is useful for us to have control over the words that appear on it.
HTML provides structure and meaning to our text, CSS allows us to precisely style it, and JavaScript contains a number of features for manipulating strings, creating custom welcome messages and prompts, showing the right text labels when needed, sorting terms into the desired order, and much more. Pretty much all of the
programs we've shown you so far in the course have involved some string manipulation. Strings are dealt with similarly to numbers at first glance, but when you dig deeper you'll start to see some
notable differences. Let's start by entering some basic lines into the browser developer console to familiarize ourselves. These lines don't work because any text without quotes around it is assumed to be a variable name, property name, a reserved word, or similar. If the browser can't find it, then an error is raised (e.g. "missing; before statement"). If the browser can see where a string starts, but can't find the end of the string, as indicated by the 2nd quote, it complains with an error (with
"unterminated string literal"). If your program is raising such errors, then go back and check all your strings to make sure you have no missing quote marks. string — try it now:
badString is now set to have the same value as string . Single quotes vs. double quotes
Escaping characters in a stringTo fix our previous problem code line, we need to escape the problem quote mark. Escaping characters means that we do something to them to make sure they are recognized as text, not part of the code. In JavaScript, we do this by putting a backslash just before the character. Try this:
This works fine. You can escape other characters in the same way, e.g. Concatenating stringsConcatenate just means "join together". To join together strings in JavaScript you can use a different type of string, called a template literal. A template literal looks just like a normal string, but instead of using single or double quote marks (
This can work just like a normal string, except you can include variables in it, wrapped inside
You can use the same technique to join together two variables:
Concatenation in contextLet's have a look at concatenation being used in action:
Here we're using the Concatenation using "+"You can also concatenate strings using the
However, template literals usually give you more readable code:
Numbers vs. stringsSo what happens when we try to combine a string and a number? Let's try it in our console:
You might expect this to return an error, but it works just fine. Trying to represent a string as a number doesn't really make sense, but representing a number as a string does, so the browser converts the number to a string and concatenates the two strings. If you have a numeric variable that you want to convert to a string but not change otherwise, or a string variable that you want to convert to a number but not change otherwise, you can use the following two constructs:
These constructs can be really useful in some situations. For example, if a user enters a number into a form's text field, it's a string. However, if you want to add this number to something, you'll need it to be a number, so you could pass it through Including expressions in stringsYou can include JavaScript expressions in template literals, as well as simple variables, and the results will be included in the result:
Multiline stringsTemplate literals respect the line breaks in the source code, so you can write strings that span multiple lines like this:
To have the equivalent output using a normal
string you'd have to include line break characters (
See our Template literals reference page for more examples and details of advanced features. ConclusionSo that's the very basics of strings covered in JavaScript. In the next article, we'll build on this, looking at some of the built-in methods available to strings in JavaScript and how we can use them to manipulate our strings into just the form we want.
In this module |