WEB Developer's Glossary

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• E-notation: JavaScript Floats
Floating point values can be defined using e-notation (exponential notation). Here a number is given followed by an "e" or "E" and this is followed by the number of times to multiply by 10.

• ECMA-262 Standard: Standard
The standard on which ECMAScript is based. See link: Standard: ECMA-262.

• ECMAScript ECMAScript
ECMAScript is a scripting language that is vendor neutral and cross-platform. ECMAScript is based on the ECMA-262 standard. Derivative languages of are JavaScript, JScript and ActionScript. The core portion of JavaScript is based on ECMAScript. See link: Standard: ECMA-262.

• Element, CSS: CSS 2.1 Specification
The element is the primary syntactic constructs of the document language. Most CSS style sheet rules use the names of these elements (such as P, TABLE, and OL in HTML) to specify how the elements should be rendered. All markup languages based on SGML will have element constructs. Extensible markup languages such as XML, will typically incorporate (define) there own unique element set.

• Element, HTML: HTML
The HTML element has a syntax defined in the HTML DTD. The syntax may comprise of an opening tag, some content and a closing tag. Depending on the element, the content may be optional and for some elements it must be EMPTY. Most people will use the terms "element" and "tag" interchangeably, but a tag is only the portion contained within the angle brackets (<>), such as <html>, whereas the element contains both opening and closing tags and the content between them. Within the HTML DTDs, the "</ELEMENT" keyword defines each element by name, start/end tag requirements and the element's content model.

• Empty Statement: JavaScript Term
The empty statement is an ECMA-262 core statement that does nothing. It has no effect and performs no action. The empty statement consists of a single stand alone semicolon. One use of the empty statement is in the header of a for statement. Each of the three expressions in the header can be empty.

• Encapsulation: JavaScript OOD
Encapsulation is one of the common OOD principles. An object combines both data and the operations of same data into a single unit that exhibits a set behavior. An object should retain the state necessary to maintain its behavior. It does this by hidding its implementation from its clients. With JS, the mechanism to allow encapsulation is the class. The other common OOD principles: abstraction, aggregation, Inheritance and polymorphism.

The ENTITY keyword is an SGML construct used in the DTD of the HTML application. They are parameter definitions that work like a macro and the definition expansion is implied everywhere the named ENTITY is referenced.

• Enumerable: JavaScript Term
The term enumerable pertains to the properties of an object. Only the local properties of an object are enumerable. Properties inherited from the prototype object are not enumerable. User defined properties are generally enumerable. The method propertyIsEnumerable, of the Object class will test whether a property is enumerable. Also, the for/in loop displays the names of properties of an object that are enumerable.

• Equality Operators: JavaScript Operator
The equality operators ( symbols: == and != ) determine wheather two operands are equivalent. When the two operands are equivalent, the equal operator returns true whereas, the not equal operator would return false. The two equality operators were designed for primitive values. However, when the operands are not of the same type, type conversions are performed before the equality check is performed.
The attributes of this operator are:

• Equality Operator Group: JavaScript Operator
The equality operator group applies to the equality operators and the identity operators. The ECMAScript Language Specification section 11.9 groups both equality operators and identity operators, thus the term.

• Errors: JavaScript Terms
A Web developer will encounter three types of errors while building client-side Web pages: 1) syntax errors, 2) logic errors and 3) run-time errors. Syntax errors are detected by the interpreter and the code is not executed. Logic errors will produce undesirable results but may not generate a run-time error. Only the run-time errors will require exception handling by the programmer. Because run-time error will normally impact the user, the developer must anticipate and design a recovery for the possible exception. Core JS has the following tools available to the programmer to recover from a run-time error:
  • Error class: the programmer can instantiate error objects through the Error class.
  • Error Object: the JS interpreter can throw an error object that can be caught by the programmer.
  • throw Statement: an exception may be explicitly thrown with the throw statement.
  • try/catch/finally Statements: these statement allow the programmer to capture an exception.

• Error Class: JavaScript Class
The JavaScript error handling is supported by one of JavaScript's Native Classes, the Error class. When an exception in JavaScript is thrown, the relevent information about the exception is stored in an Error object. The JavaScript programmer can also create Error instances with the Error class constructor for the purpose of capturing the run-time exceptions. The Error class is a unique class in that it is the only native class that acts as both a subclass and a super class. Acting as a subclass, the Error class inherits from the Object super class. Acting as a super class, the Error class serves the rest of the error subclasses (EvalError, RangeError, ReferenceError, SyntaxError, TypeError, URIError).

• Error Object: JavaScript Object
The Error object is a instance of the Error class. An Error object can be declared and initialized via the Error class constructor. JS never throws an Error object directly; instead, it throws instances of one of the error subclasses. See our link for class for the distinction between the terms "class" and "object".

• Escape Sequence: JavaScript RegExp
The general definition for the string escape_sequence holds true for regular expressions. However, with regular expression patterns, additional considerations apply. The regular expression meta characters and some regular expression literal characters must be escaped.

• Escape Sequence: CSS, JavaScript String
When a backslash ( \ ) is encountered in a string of characters, the next character is combined with the backslash to form an escape sequence. The interpreter allows an escape from the normal interpretation of the character and performs an entirely different function. JS supports a predefined escape sequence set of characters. A backslash preceding any character not in this set is ignored by the interpreter.

• EvalError Subclass: JavaScript Class
The JS interpreter can throw an instance of the EvalError subclass when the function eval() was called illegally. The JavaScript programmer can also create EvalError instances with the EvalError class constructor for the purpose of capturing the run-time exceptions. The EvalError subclass inherits from the Error class that acts as a super class. The complete set of error subclasses are: EvalError, RangeError, ReferenceError, SyntaxError, TypeError, URIError.

• Explicit Assignment: JavaScript Statement
An explicit assignment statement incorporates the var keyword prior to the variable name. However, the the var keyword is not mandatory with the assignment statement. The primary consideration as to whether to use the var keyword is one of scope. A variable assignment without the var keyword (implicit assignment) will always have global scope. A variable assigned explicitly will receive the scope appropriate for it's immediate container. A variable at top level code will receive global scope. A variable within a function with receive local scope.

• Expressions: JavaScript Expression
An expression in JavaScript is a phrase that will be evaluated by the interpreter to a single value. Simple expressions are used as operands to an operator. Simple expressions are used in statements such as the return statement, switch statement, looping statements, etc. The ECMA-262 standard classifies all JS operators (accompanied by there operands) as expressions.

• Expression Statement: JavaScript Statement
An expression statement is a stand alone executable. Unlike typical core JS statements, the expression statement always involves an operator. The expression statement does create a side effect but may or may not return a value. The expression statement is a hybrid of the simple expression and a JS statement. They are a statement because they cause a side effect and end with a semicolon. They are an expression because they include an operator. Some examples of expression statements are: assignment statements, delete statements, void statements and increment and decrement statements.

• External or Global Reference: Web
A reference to the absolute location of the resource on the Web. This hyperlink's destination is normally outside the current Web site's location.


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