JS Learning the fourth day----optional semicolon

Optional semi-colon

As in some languages,, JSusing semicolons(;)separate the statements.This is important to enhance the readability and cleanliness of your code.:missing delimiter,The end of a statement is the next statement,you seem to be talking to someone on the walkie-talkie.,I didn't finish a word.,have to say Oversame,It means you're done..in theJSin,if the statements are exclusive to each row,patency can omit a semicolon between statements.manyJSthe programmer uses semicolons to explicitly mark the end of a statement,It is also true when a semicolon is fully needed in propane.another style is,omit it in any place where it can be omitted.,use semicolons only when you have to use them..whatever it takes to become a style,about theJSThere are a few things to be aware of in the optional semicolon.

Case :

A=3;

b=4;

Analysis : Since two statements are written in two lines , the first semicolon , that is to say , the semicolon of the a=3 sentence can be omitted .

But if you write this :

a=3;b=4;

Analysis : This will not omit the first semicolon.

It is important to note that JS does not fill the semicolon at all line breaks : js will fill the semicolon only if the code is not parsed correctly when the semicolon is missing. . In other words, , if the current statement and subsequent non-whitespace characters cannot be interpreted as a whole , JS fills the semicolon at the end of the current statement line . Case :

var a

A

=

3

Console.log (a)

JS interprets it as :

var a;a=3;console.log (a);

JS adds a semicolon to the first line of line breaks , because if there is no semicolon , JS cannot parse the code var A. a second a can be treated as a single statement "a"; but , JS and did not give the second line the end of the fill semicolon , because he can parse it into "A=3" with the third line of content.

I do not know that handsome man (SB) invented this situation , We are still the old honest line statement a semicolon . try not to engage in heinous acts. . I say these questions so that you can read the code that someone else wrote. , after all, a wonderful day , very much today . .

The segmentation rules for these statements lead to unexpected situations , which are written in two lines and appear to be two separate statements :

var y=x+f

(A+B). ToString ()

But the second line of parentheses and the first line of F make up a function call , JS will consider this code :

var y=x+f (a+b). toString ();

This is not the case for the northern part of this code . in order to allow the above code to parse into two different statements , You must manually fill in the display semicolon at the end of the line .

Generally speaking,If a statement"(", "[", "/", "+" or "-" start,then it is very likely to parse with the previous set of statements.in"/", "+" and "-" are uncommon for statements that start with,the person who writes this code is far better off..but with"(" and "[" Start with a lot of statements,At least inJSis very common in the.Some more cautious programmers prefer to add a semicolon to the front of the statement,This is done to avoid forgetting the semicolon of the previous statement.Case:

var x=0// Forget the semicolon here

; [X,x+1,x+2].foreach (Console.log);// The semicolon in front ensures correct parsing of the statement

If the current statement and the next line of statements cannot be parsed , JS fills the semicolon after the first line , which is a general rule , with two exceptions . The first exception is in relation to Return,break and the Continue statement in the scene . If these three keywords are followed by a newline , JS The semicolon is filled in a newline. . Case :

Return

True

Analysis : JS will parse into : return; true; , but JS 's intention is to return true;

that is, There can be no line break between Return,break, and continue and subsequent expressions . If a line break is added , The program will only get an error if it is in very special circumstances. , and the program is very inconvenient to debug .

The second exception really involves the time of the "+ +" and "--" operators . These operators can be prefixed with an expression , can also be used as the suffix of an expression . If you use it as a suffix expression , He and the expression should be on the same line . otherwise , end of line will fill the semicolon , at the same time "+ +" or "-" will be used as the prefix operator for the next generation of code and parse it together , case :

X

++

Y

This code will be parsed as " x;++y" instead of " x++;y".

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JS Learning the fourth day----optional semicolon