In modern JavaScript, there are two types of numbers:
Regular numbers in JavaScript are stored in 64… The same is true for most large numbers.… In other words, a negative number after "e" means a division by 1 with the given number of… A few examples:
Math.random()
Returns a random number from 0 to 1 (not including 1).… A negative number after "e" causes the number to be divided by 1 with given zeroes.
Below, makeCounter creates the “counter” function that returns the next number on each invocation:… Despite being simple, slightly modified variants of that code have practical uses, for instance, as a random… number generator to generate random values for automated tests.
For instance, an unending sequence of pseudo-random numbers.… For instance, we have a function that generates a sequence of numbers:
Sec-WebSocket-Key – a random browser-generated key, used to ensure that the server supports WebSocket… It’s random to prevent proxies from caching any following communication.
methods that use it is unpredictable, e.g. document.getElementById may return any of such elements at random
the end of an integer literal or by calling the function BigInt that creates bigints from strings, numbers… Math operators.BigInt can mostly be used like a regular number, for example:… We can’t mix bigints and regular numbers:… () to convert a bigint to a number.… This library implements big numbers using its own methods.
Let’s say we have a string like +7(903)-123-45-67 and want to find all numbers in it.… A number is a sequence of 1 or more digits \d.… Quantity {n}.The simplest quantifier is a number in curly braces: {n}.… A number is a sequence of one or more digits in a row.… Regexp for decimal fractions (a number with a floating point): \d+\.
The number type represents both integer and floating point numbers.… It is a special value that’s greater than any number.… We’ll see more about working with numbers in the chapter Numbers.… Read it when you need such big numbers.… Seven primitive data types:
number for numbers of any kind: integer or floating-point, integers are
JavaScript allows us to work with primitives (strings, numbers, etc.) as if they were objects.… There are 7 primitive types: string, number, bigint, boolean, symbol, null and undefined.… The language allows access to methods and properties of strings, numbers, booleans and symbols.… A number has methods of its own, for instance, toFixed(n) rounds the number to the given precision:… They convert a value to the corresponding type: to a string, a number, or a boolean (primitive).
Mathematical operations convert values to numbers.… If the string is not a valid number, the result of such a conversion is NaN.… Otherwise, the number is “read” from the string. An error gives NaN.… Summary.The three most widely used type conversions are to string, to number, and to boolean.… Can be performed with Number(value).
Usually, the plus operator + sums numbers.… Other arithmetic operators work only with numbers and always convert their operands to numbers.… But if the operand is not a number, the unary plus converts it into a number.… Every operator has a corresponding precedence number.… The one with the larger number executes first.
Int8Array, Int16Array, Int32Array – for signed integer numbers (can be negative).… It saves 255 for any number that is greater than 255, and 0 for any negative number.… The i-th number is arr[i].… Int8Array, Int16Array, Int32Array – for signed integer numbers (can be negative).… Float32Array, Float64Array – for signed floating-point numbers of 32 and 64 bits.
For instance, binary plus + can work both with strings (concatenates them) and numbers (adds them).… The greater and less comparison operators, such as < >, can work with both strings and numbers… Still, they use the "number" hint, not "default".… for the hint "number".… Then "2" * 2 becomes 2 * 2 (the string is converted to number).
If we want a number, we can use \d+.… The first number \d+ has 7 digits, and then a number of 2 digits:… The first number has 7 digits, and then two numbers of 1 digit each:… The first number has 6 digits, and then a number… The first is to lower the number of possible combinations.
That is: a number, followed by € sign.
Lookahead.The syntax is: X(?… For an integer number followed by €, the regexp will be \d+(?… That’s a number \d+, NOT followed by €.
For that, a negative lookahead can be applied.… The dollar sign is usually before the number, so to look for $30 we’ll use (?… That’s natural: we look for a number \d+, while (?
And Number property means that it’s a digit: maybe Arabic or Chinese, and so on.… Number N:
decimal digit Nd,
letter number Nl,
other No.… Nl (e.g. Ⅻ – a character for the roman number 12), plus some other symbols Other_Alphabetic (OAlpha)… Example: hexadecimal numbers.For instance, let’s look for hexadecimal numbers, written as xFF, where… and {n} we’ll see how to look for numbers that contain many digits.
value:
There are 8 data types:
number… for both floating-point and integer numbers,
bigint for integer numbers of arbitrary length,
string… Comparisons
Equality check == for values of different types converts them to a number (except null and… Other comparisons convert to a number… Greater/less comparisons compare strings character-by-character, other types are converted to a number
In this case the numbering also goes from left to right.… Then groups, numbered from left to right by an opening paren.… Named groups.Remembering groups by their numbers is hard.… That’s done using $n, where n is the group number.… A group may be excluded from numbering by adding ?: in its start.
new Date(milliseconds)
Create a Date object with the time equal to number… An integer number representing the number of milliseconds that has passed since the beginning of 1970… , date diff.When a Date object is converted to number, it becomes the timestamp same as date.getTime(… The call to Date.parse(str) parses the string in the given format and returns the timestamp (number of… That’s because a Date becomes the timestamp when converted to a number.
Consider a practical task – we have a phone number like "+7(903)-123-45-67", and we need to… turn it into pure numbers: 79031234567.… To do so, we can find and remove anything that’s not a number.… For instance, let’s find the first digit in the phone number:… In the beginning of the chapter we saw how to make a number-only phone number from a string like +7(903
We can use both the name or the number in the document to get the form.… subelements,
select.value – the value of the currently selected <option>,
select.selectedIndex – the number… If we know the new option number: set select.selectedIndex to that number.… Option elements have properties:
option.selected
Is the option selected.
option.index
The number
For example, the pattern \b\d\d\b looks for standalone 2-digit numbers.… In other words, it looks for 2-digit numbers that are surrounded by characters different from \w, such
Comparison of different types.When comparing values of different types, JavaScript converts the values to numbers… This happens because operands of different types are converted to numbers… For maths and other comparisons < > <= >=
null/undefined are converted to numbers: null… Comparisons convert null to a number, treating it as 0.… When values of different types are compared, they get converted to numbers (with the exclusion of a strict
Backreference by number: \N.A group can be referenced in the pattern using \N, where N is the group number
Many JavaScript built-in functions support an arbitrary number of arguments.… Rest parameters ....A function can be called with any number of arguments, no matter how it is defined… For instance, there’s a built-in function Math.max that returns the greatest number from a list:… Use patterns:
Rest parameters are used to create functions that accept any number of arguments.
…So the engine decreases the number of repetitions of .+ by one more character:… It means: “repeat minimal number of times”.
We can enable it by putting a question mark '?'… Then the regular expression engine increases the number of repetitions for the dot and tries one more… work the similar way – the regexp engine increases the number of repetitions only if the rest of the… If there’s no match then it decreases the number of repetitions (backtracks) and tries again.
its value.
clear() – delete everything.
key(index) – get the key on a given position.
length – the number… If they were any other type, like a number, or an object, they would get converted to a string automatically… removeItem(key) – remove the key with its value.
clear() – delete everything.
key(index) – get the key number… index.
length – the number of stored items.
JSON supports following data types:
Objects { ... }
Arrays [ ... ]
Primitives:
strings,
numbers,
boolean… Formatting: space.The third argument of JSON.stringify(value, replacer, space) is the number of spaces… In this case, the string is used for indentation instead of a number of spaces.… JSON supports plain objects, arrays, strings, numbers, booleans, and null.
For example, outputting goods from a list one after another or just running the same code for each number… For example, the loop below asks the user for a series of numbers, “breaking” when no number is entered… directive stops executing the body and passes control to the next iteration of for (with the next number
the brackets:
Array elements are numbered… We can get an element by its number in square brackets:… That’s essentially the same as obj[key], where arr is the object, while numbers are used as keys.… If new Array is called with a single argument which is a number, then it creates an array without items… declaration:
The call to new Array(number
For a number, it will be [object Number]
For a boolean, it will be [object Boolean]
For null: [object
The “length” property.There is another built-in property “length” that returns the number of function… For instance, in the code below the ask function accepts a question to ask and an arbitrary number of… if there’s none, JavaScript tries to guess it from the context (e.g. an assignment).
length – the number
We could also start it from somewhere in the middle of the transition, from an exact number… Steps.The timing function steps(number of steps[, start/end]) allows splitting an transition into multiple… The first argument of steps(9, start) is the number… For instance, width, color, font-size are all numbers.… When you animate them, the browser gradually changes these numbers frame by frame, creating a smooth
The syntax is:
It accepts any number… return:
For instance, to sort as numbers… It may contain numbers or strings or objects or whatever. We have a set of some items.… A comparison function may return any number
Actually, a comparison function is only required… to return a positive number to say “greater” and a negative number to say “less”.
In hello.js, click at line number 4. Yes, right on the 4 digit, not on the code.
Congratulations!… Please also click on the number for line 8.… Conditional breakpoints
Right click on the line number allows to create a conditional breakpoint
Primitives.The most intricate thing happens with strings, numbers and booleans.… access their properties, temporary wrapper objects are created using built-in constructors String, Number
for 3, the result of the prompt is a string "3", which is not strictly equal === to the number
That may be even a primitive, like a number or a string, but it’s better to use objects, preferably with… For instance, we want to measure the time that a Fibonacci numbers function fib(n) takes.… particular, the implementation of fib(n) in the code below returns an error for negative or non-integer numbers… message
Error message.
url
URL of the script where error happened.
line, col
Line and column numbers
For instance, the number 1 is treated as true, the number 0 as false:
It says what’s inside the variable: a string, a number or something else.… Which string/number does it store?
There’s just no way to figure out without a good meditation!… Just add a number: data1, item2, elem5…
Attention test.Only a truly attentive programmer should be
them are called “primitive”, because their values contain only a single thing (be it a string or a number… For instance, a number 0 becomes a string "0" when used as a property key:… So, "49" is an integer property name, because when it’s transformed to an integer number and
Now it works with any number… of arguments (though the hash function would also need to be adjusted to allow any number of arguments… It would be better if it could glue any number of args.
And keep their number at minimum.
Like a range object that represents an interval of numbers:… Or we can make an iterable object that generates an infinite sequence of pseudorandom numbers.
To resume upload, we need to know exactly the number of bytes received by the server.
methods that allow to get the character for the code and back:
str.codePointAt(pos)
Returns a decimal number… whether str is less, equal or greater than str2 according to the language rules:
Returns a negative number… Returns a positive number if str is greater than str2.
Returns 0 if they are equivalent.
given <tr> inside the enclosing <thead>/<tbody>/<tfoot>.
tr.rowIndex – the number… <td> and <th>:
td.cellIndex – the number of the cell inside the enclosing <tr>.
On the right, there is a clickable link to the source bug.html:12 with the line number where the error
Additionally, the header Access-Control-Max-Age may specify a number of seconds to cache the permissions… If there’s the header Access-Control-Max-Age with a number of seconds, then the preflight permissions… methods,
Access-Control-Allow-Headers with a list of allowed headers,
Access-Control-Max-Age with a number
For example, Math.trunc(n) is a function that “cuts off” the decimal part of a number, e.g Math.trunc
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