Viewing: ar.javascript.info

if ?, .

if

if(...) true, .

let year = prompt('       ECMAScript-2015?', '');

if (year == 2015) alert( ' !' );

(year == 2015), .

          if (year == 2015) {
    alert(" !");
    alert(" !");
}
        

{} if . .

if () .

0, "", null, undefined, NaN false. falsy .
true, truthy.

          if (0) { // 0  falsy
  ...
}
        

          if (1) { // 1  truthy
  ...
}
        

if, :

          let cond = (year == 2015); //    true  false

if (cond) {
  ...
}
        

else

if else . false.

let year = prompt("       ECMAScript-2015?", "");

if (year == 2015) {
    alert(" !");
} else {
    alert("    "); // any value except 2015
}

: else if

. else if .

let year = prompt("       ECMAScript-2015?", "");

if (year < 2015) {
    alert(" ");
} else if (year > 2015) {
    alert(" ");
} else {
    alert("");
}

, year < 2015. , year > 2015. alert.

else if . else .

?

let accessAllowed;
let age = prompt('  ', '');

if (age > 18) {
  accessAllowed = true;
} else {
  accessAllowed = false;
}

alert(accessAllowed);

?. ternary 3 . .

let result = condition ? value1 : value2;

condition value1 value2.

let accessAllowed = age > 18 ? true : false;

age > 18. >.

          //   "age > 18"  
// (    )
let accessAllowed = age > 18 ? true : false;
        

true/false:

          // 
let accessAllowed = age > 18;
        

?

? .

let age = prompt("", 18);

let message =
    age < 3
        ? "  !"
        : age < 18
        ? "!"
        : age < 100
        ? "!"
        : "     !";

alert(message);

age < 3.
' !'. ':' age < 18.
'!'. ':' age < 100.
'!'. ':' ' !'.

if..else:

          if (age < 3) {
    message = "  !";
} else if (age < 18) {
    message = "!";
} else if (age < 100) {
    message = "!";
} else {
    message = "     !";
}
        

?

? if:

let company = prompt('     ', '');

(company == 'Netscape') ?
   alert('!') : alert('.');

company == 'Netscape', ? .

if .

if :

let company = prompt('     ', '');

if (company == 'Netscape') {
  alert('!');
} else {
  alert('.');
}

. .

? . . if .

if ( )

alert

          if ("0") {
  alert( '' );
}
        

"0" ) true .

if ("0") {
  alert( '' );
}

if..else, :

ECMAScript, !, : ECMAScript!

[]

<!DOCTYPE html>
<html>

<body>
  <script>
    'use strict';

    let value = prompt('      ', '');

    if (value == 'ECMAScript') {
      alert('!');
    } else {
      alert("   ECMAScript!");
    }
  </script>


</body>

</html>

if..else prompt alert:

1, ,
-1, ,
0, .

let value = prompt(' ', 0);

if (value > 0) {
  alert( 1 );
} else if (value < 0) {
  alert( -1 );
} else {
  alert( 0 );
}

'if' '?'

if '?':

          let result;

if (a + b < 4) {
    result = "";
} else {
    result = "";
}
        

let result = (a + b < 4) ? '' : '';

'if..else' '?'

if..else '?'.

          let message;

if (login == "Employee") {
    message = "";
} else if (login == "Director") {
    message = "";
} else if (login == "") {
    message = " ";
} else {
    message = "";
}
        

          let message = (login == 'Employee') ? '' :
  (login == 'Director') ? '' :
  (login == '') ? ' ' :
  '';
        

: if, '?'