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1-js/02-first-steps/16-javascript-specials/article.md
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# JavaScript specials
This chapter aims to list features of JavaScript that we've learned, paying special attention to subtle moments.
That's especially useful if you came from another language or just as a recap.
This chapter briefly recaps the features of JavaScript that we've learned by now, paying special attention to subtle moments.
[cut]
@ -31,14 +29,16 @@ alert("There will be an error after this message")
Most codestyle guides agree that we should put a semicolon after each statement.
Semicolons are not required after code blocks `{...}` and syntax constructs with them:
Semicolons are not required after code blocks `{...}` and syntax constructs with them like loops:
```js
function f() {
// no semicolon needed after function declaration
}
for(;;) { /* no semicolon after the loop */ }
for(;;) {
// no semicolon needed after the loop
}
```
...But even if we can put an "extra" semicolon somewhere, that's not an error, it will be ignored.
@ -59,7 +59,7 @@ The directive must be at the top of a script or at the beginning of a function.
Without `"use strict"`, everything still works, but some features behave in old-fasion, "compatible" way. We'd generally prefer the modern behavior.
Advanced features of the language (like classes that we'll study in the future) that enable strict mode implicitly.
Some modern features of the language (like classes that we'll study in the future) enable strict mode implicitly.
More in: <info:strict-mode>.
@ -67,8 +67,8 @@ More in: <info:strict-mode>.
Can be declared using:
- `let` (block-level visibility)
- `const` (can't be changed)
- `let`
- `const` (constant, can't be changed)
- `var` (old-style, will see later)
A variable name can include:
@ -92,7 +92,7 @@ There are 7 data types:
- `undefined` -- a type with a single value `undefined`, meaning "not assigned",
- `object` and `symbol` -- for complex data structures and unique identifiers, we didn't learn them yet.
The `typeof` operator returns the type for a value, with two special behaviors:
The `typeof` operator returns the type for a value, with two exceptions:
```js
typeof null == "object" // error in the language
typeof function(){} == "function" // functions are treated specially
@ -125,7 +125,7 @@ alert( "Visitor: " + userName ); // Alice
alert( "Tea wanted: " + isTeaWanted ); // true
```
More in: <info:uibasic>.
More in: <info:alert-prompt-confirm>.
## Operators
@ -134,9 +134,7 @@ JavaScript supports following operators:
Arithmetical
: Regular: `* + - /`, also `%` for the remainder and `**` for power of a number.
Binary plus `+` concatenates strings.
If any of the operands is a string -- the other one is converted to string too:
Binary plus `+` concatenates strings. And if any of the operands is a string -- the other one is converted to string too:
```js run
alert( '1' + 2 ); // '12', string
@ -147,11 +145,10 @@ Assignments
: There is a simple assignment: `a = b` and combined ones like `a *= 2`.
Bitwise
: Bitwise operators work with integers on bit-level: see the [docs](mdn:JavaScript/Refereno
ce/Operators/Bitwise_Operators) when they are needed.
: Bitwise operators work with integers on bit-level: see the [docs](mdn:/JavaScript/Reference/Operators/Bitwise_Operators) when they are needed.
Ternary
: The only operator with three parameters: `cond ? resultA : result B`
: The only operator with three parameters: `cond ? resultA : result B`. If `cond` is truthy, returns `resultA`, otherwise `resultB`.
Logical operators
: Logical AND `&&` and OR `||` perform short-circuit evaluation and then return the value where it stopped.
@ -168,8 +165,6 @@ Comparisons
The strict equality operator `===` doesn't do the conversion: different types always mean different values for it, so:
Values `null` and `undefined` are special: they equal `==` each other and don't equal anything else.
Greater/less comparisons compare strings character-by-character, other types are converted to a number.
@ -177,7 +172,7 @@ Comparisons
Logical operators
: There are few others, like a comma operator.
More in: <info:operators>, <info:comparison>, <info:logical-ops>.
More in: <info:operators>, <info:comparison>, <info:logical-operators>.
## Loops
@ -218,7 +213,7 @@ let age = prompt('Your age?', 18);
switch (age) {
case 18:
alert("Won't work"); // the result of prompt is a string, not a number
alert("Won't work"); // the result of prompt is a string, not a number
case "18":
alert("This works!"");
@ -291,6 +286,4 @@ More: see <info:function-basics>, <info:function-expressions-arrows>.
## More to come
That was a brief list of JavaScript specials that we need to know to code well.
As of now that were only basics. Further in the tutorial you'll find more specials and advanced features of JavaScript.
That was a brief list of JavaScript features. As of now we studied only basics. Further in the tutorial you'll find more specials and advanced features of JavaScript.