JavaScript . .

UTF-16, .

.

, :

let single = '-';
let double = "-";

let backticks = `-`;

. - , ${}:

function sum(a, b) {
  return a + b;
}

alert(`1 + 2 = ${sum(1, 2)}.`); // 1 + 2 = 3.

, :

let guestList = `:
 * 
 * 
 * 
`;

alert(guestList); //     

, ? .

, :

let guestList = ": // : Unexpected token ILLEGAL
  * ";

, . .

. : func`string`. func , . , , MDN: Template literals.

, \n, :

let guestList = ":\n * \n * \n * ";

alert(guestList); //     ,   

, , -:

let str1 = "\n"; //     "  "

//          
let str2 = `
`;

alert(str1 == str2); // true

, .

\. .

, \ , :

alert( ` : \\` ); //  : \

\', \", \` , .

:

alert( '\'   !' ); // '   !

, \', .

, , . :

alert( `'   !` ); // '   !

, Unicode \u, Unicode.

length :

alert( `\n`.length ); // 4

, \n , 4.

, pos, : [pos], str.at(pos). :

let str = ``;

//  
alert( str[0] ); // 
alert( str.charAt(0) ); // 

//  
alert( str[str.length - 1] ); // 
alert( str.at(-1) ); // 

, .at(pos) , . pos , .

, .at(-1) , .at(-2) , .

undefined , :

let str = ``;

alert( str[-2] ); // undefined
alert( str.at(-2) ); // 

, for..of:

for (let char of "") {
  alert(char); // ,,,,, (char   "",  "",  ""   )
}

JavaScript . .

:

let str = '';

str[0] = ''; // 
alert( str[0] ); //  ,      

, .

:

let str = '';

str = '' + str[1]; //  

alert( str ); // 

.

toLowerCase() toUpperCase() :

alert( ''.toUpperCase() ); // 
alert( ''.toLowerCase() ); // 

:

alert( 'Interface'[0].toLowerCase() ); // ''

.

str.indexOf

str.indexOf(substr, pos).

substr str, pos, , , , -1.

:

let str = '  ';

alert( str.indexOf('') ); // 0,   ''    
alert( str.indexOf('') ); // -1,   ,    

alert( str.indexOf("") ); // 1,  ""    1 (..  )

pos .

, "" 1. , 2:

let str = '  ';

alert( str.indexOf('', 2) ) // 9

, indexOf . :

let str = ',  , ,  ';

let target = ''; //   

let pos = 0;
while (true) {
  let foundPos = str.indexOf(target, pos);
  if (foundPos == -1) break;

  alert( ` : ${foundPos}` );
  pos = foundPos + 1; //    
}

:

let str = ",  , ,  ";
let target = "";

let pos = -1;
while ((pos = str.indexOf(target, pos + 1)) != -1) {
  alert( pos );
}

indexOf if. if :

let str = "  ";

if (str.indexOf("")) {
    alert(" "); //  
}

alert , str.indexOf("") 0 ( , ). , if , 0 false.

-1, :

let str = "  ";

if (str.indexOf("") != -1) {
    alert(" "); //  !
}

includes, startsWith, endsWith

str.includes(substr, pos) true/false substr str.

, , :

alert( "  ".includes("") ); // true

alert( "".includes("") ); // false

pos :

alert( "".includes("") ); // true
alert( "".includes("", 3) ); // false,   3- ,  "" 

, str.startsWith str.endsWith , .

alert( "".startsWith("") ); // true, ""   ""
alert( "".endsWith("") ); // true, ""   ""

JavaScript 3 : substring, substr slice.

str.slice(start [, end])

start ( ) end.

:

let str = "stringify";
alert( str.slice(0, 5) ); // 'strin',   0  5 (5  )
alert( str.slice(0, 1) ); // 's',  0  1,  1  ,      0

, slice :

let str = "stringify";
alert( str.slice(2) ); // 'ringify',   2   

start/end . , :

let str = "stringify";

//   4-  ,    1-  
alert( str.slice(-4, -1) ); // 'gif'

str.substring(start [, end])

start end ( end).

slice, substring start , end ( start end ).

:

let str = "stringify";

//  substring    
alert( str.substring(2, 6) ); // "ring"
alert( str.substring(6, 2) ); // "ring"

// ...   slice:
alert( str.slice(2, 6) ); // "ring" ( )
alert( str.slice(6, 2) ); // "" ( )

( slice) , 0.

str.substr(start [, length])

start, length.

, length :

let str = "stringify";
alert( str.substr(2, 4) ); // 'ring',    2  4 

, :

let str = "stringify";
alert( str.substr(-4, 2) ); // 'gi',    4    2 

Annex B . , Javascript, . .

:

, .

, .

1. :

   alert( 'a' > 'Z' ); // true

2. :

   alert( 'sterreich' > 'Zealand' ); // true

   , . , Zealand sterreich.

, , , JavaScript UTF-16. , .

, .

str.codePointAt(pos)

, pos:

//       
alert( "z".codePointAt(0) ); // 122
alert( "Z".codePointAt(0) ); // 90
alert( "z".codePointAt(0) ); // 122
alert( "z".codePointAt(0).toString(16) ); // 7a (       )

String.fromCodePoint(code)

code

alert( String.fromCodePoint(90) ); // Z
alert( String.fromCodePoint(0x5a) ); // Z (       )

65..220 ( ), :

let str = '';

for (let i = 65; i <= 220; i++) {
  str += String.fromCodePoint(i);
}
alert( str );
// alert :
// ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~
// 

? , , .

, a > Z.

. , . a (97) Z (90).

• , .
• , - , . - a z.

, , .

, .

, ECMA-402.

, .

str.localeCompare(str2) , , str , str2 :

• , str , str2.
• , str , str2.
• 0, .

:

alert( 'sterreich'.localeCompare('Zealand') ); // -1

, , ( . ), , - "a" "a".

• 3 . ${}.
• , \n.
• , : [] at.
• , : slice substring.
• / , : toLowerCase/toUpperCase.
• , : indexOf, includes/startsWith/endsWith .
• , localeCompare, .

:

• str.trim() () .
• str.repeat(n) n .
• .

/ . , .

, , Unicode, , . Unicode , .