Once the control comes across a condition that is true, rest of the else if blocks are skipped. surround it, even after it leaves the scope in which it was created. JavaScript did not have exception handling until ECMAScript 3, which explains why the language so often automatically converts values and so often fails silently: it initially couldn’t throw exceptions. This section does not fully explain how JavaScript inheritance works, but it shows you a simple pattern to get you started. This section gives a little background on JavaScript to help you understand why it is the way it is. In other languages, you learn language features. The following values are interpreted as false: All other values (including all objects!) We mainly use JavaScript to create * websites * web applications * server-side applications using Node.js but JavaScript is not limited to these things, and it can also be used to * create mobile applications using tools like … programming languages may benefit from learning about some of the peculiarities of JavaScript. To insert few words of code, use the
tag, for several lines – wrap them in tag, for more than 10 lines – use a sandbox (plnkr, jsbin, codepen…) Similarly, -Infinity is smaller than any other number (except NaN). If you have suggestions what to improve - please submit a GitHub issue or a pull request instead of commenting. and object-oriented programming (objects, inheritance). Each variable declaration is hoisted: the declaration is moved to the beginning of the function, but assignments that it makes stay put. Otherwise, return the second operand: first operand is truthy, return it. Constructors are thus a rough analog to classes in other languages. For ", "Hang tight in there. • JavaScript can dynamically modify an HTML page • JavaScript can react to user input • JavaScript can validate user input • JavaScript can be used to create cookies (yum!) Tutorial map. They are function arguments, the right side of an assignment, etc. It is called IIFE (immediately invoked function expression, pronounced “iffy”): Be sure to type the preceding example exactly as shown (apart from the comments). This is inconvenient if you nest a function inside a method, because you can’t access the method’s this from the function. Math (see Chapter 21) is an object with arithmetic functions. Lizenz: Creative Commons Namensnennung - Weitergabe unter gleichen Bedingungen. Here is an example of a statement, which declares (creates) a variable foo: var foo; Otherwise, return the second operand: Normal equality considers (too) many values to be equal (the details are explained in Normal (Lenient) Equality (==, !=)), which can hide bugs. All numbers in JavaScript are floating-point: Infinity is larger than any other number (except NaN). Either of the two sets of statements shall be executed for sure based on the condition. You can read (“get”) and write (“set”) properties: Function-valued properties such as describe are called methods. It will, however, make all parameters available via the special variable arguments. JavaScript has two such “nonvalues,” undefined and null: undefined means “no value.” Uninitialized variables are undefined: If you read a nonexistent property, you get undefined: undefined and null have no properties, not even standard methods such as toString(). It has a property length, and you can access its elements via indices in square brackets. Next if condition is evaluated. • JavaScript is a full-featured programming language • JavaScript user interaction does not require any communication with the server In this example, x is defined as a variable. It creates a new function whose this always has the given value: Every function has its own special variable this. You had a wonderful weekend. Strings are concatenated via the plus (+) operator, which converts the other operand to a string if one of the operands is a string: To concatenate strings in multiple steps, use the += operator: Strings have many useful methods (see String Prototype Methods). At the moment, Mozilla is one of the few companies allowed to officially use the name. To include JavaScript inside a page, you need to wrap it in