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Introduction to JavaScript (JavaScript 1) Xingquan (Hill) Zhu xqzhu@cse.fau

Introduction to JavaScript (JavaScript 1) Xingquan (Hill) Zhu xqzhu@cse.fau.edu. JS. Introduction General Syntactic Characteristics JS write to the XHTML document Write vs Writeln Typical JS dialogs Primitives, Operations, & Expressions Primitives: Number, String, Boolean, Undefined, Null

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Introduction to JavaScript (JavaScript 1) Xingquan (Hill) Zhu xqzhu@cse.fau

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  1. Introduction to JavaScript(JavaScript 1)Xingquan (Hill) Zhuxqzhu@cse.fau.edu JS

  2. JS • Introduction • General Syntactic Characteristics • JS write to the XHTML document • Write vs Writeln • Typical JS dialogs • Primitives, Operations, & Expressions • Primitives: Number, String, Boolean, Undefined, Null • Numeric operators • String catenation • Coercions • Control Statements • Selection statements • Loop statements JS

  3. Introduction • JavaScript scripting language • Enhance functionality and appearance • Client-side scripting • Make pages more dynamic and interactive • Foundation for complex server-side scripting • Program development • Program control JavaScript Examples JS

  4. Things you should know about JS • JavaScript can be used to replace some of what is typically done with applets (except graphics) • JavaScript can be used to replace some of what is done with CGI (but no file operations or networking) • User interactions through forms are easy • The Document Object Model (DOM) makes it possible to support dynamic HTML documents with JavaScript • Event-Driven Computation • User interactions with HTML documents in JavaScript use the event-driven model of computation • User interactions with form elements can be used to trigger execution of scripts JS

  5. Things you should know about JS • JavaScript is NOT an object-oriented programming language • Does not support class-based inheritance • Cannot support polymorphism • Has prototype-based inheritance, which is much different • JavaScript Objects • JavaScript objects are collections of properties, which are like the members of classes in Java and C++ • Date.getTime() • JavaScript has primitives for simple types • All JavaScript objects are accessed through references JS

  6. General Syntactic Characteristics • For this book, all JavaScript scripts will be embedded in HTML documents • Either directly, as in <script type = “text/javaScript"> -- JavaScript script – </script> • Or indirectly, as a file specified in the src attribute of <script>, as in <script type = "text/javaScript" src = "myScript.js"> </script> Example JS

  7. General Syntactic Characteristics • Identifier form: begin with a letter or underscore, followed by any number of letters, underscores, and digits • Case sensitive • variable1 and Variable1 are different • 25 reserved words, plus future reserved words • - Comments: both // and /* … */ JS

  8. General Syntactic Characteristics • Scripts are usually hidden from browsers that do not include JavaScript interpreters by putting them in special comments <!— -- JavaScript script – //--> • Semicolons can be a problem • They are “somewhat” optional • Problem: When the end of the line CAN be the end of a statement – JavaScript puts a semicolon there Return X; JS

  9. JS • Introduction • General Syntactic Characteristics • JS write to the XHTML document • Write vs Writeln • Typical JS dialogs • Primitives, Operations, & Expressions • Primitives: Number, String, Boolean, Undefined, Null • Numeric operators • String catenation • Coercions • Control Statements • Selection statements • Loop statements JS

  10. Simple Program: Printing a line of text in a web page <html xmlns = "http://www.w3.org/1999/xhtml"> <head> <title>A First Program in JavaScript</title> <script type = "text/javascript"> <!-- document.writeln("<h1>Welcome to JavaScript Programming!</h1>" ); // --> </script> </head><body></body> </html> Example JS

  11. Write vs Writeln • Document.writeln(“This is the end!”) • Document.write(“This is the end!\r\n”); Example2Example 3 Want to know what was written to the browser? Mozilla Script Tracer http://www.netamo.com/tracer JS

  12. JS

  13. Typical JS dialogs • “Window” object • JavaScript model for the browser window • Three methods: Prompt, confirm, alert • Cause the browser to wait for a user response Example alert, confirm, prompt JS

  14. Number • parseInt(variable); • parseFloat(variable); Example JS

  15. JS • Introduction • General Syntactic Characteristics • JS write to the XHTML document • Write vs Writeln • Typical JS dialogs • Primitives, Operations, & Expressions • Primitives: Number, String, Boolean, Undefined, Null • Numeric operators • String catenation • Coercions • Control Statements • Selection statements • Loop statements JS

  16. Primitives, Operations, & Expressions • Five primitive types Example • Number, String, Boolean, Undefined, or Null • JavaScript is dynamically typed – any variable can be used for anything (primitive value or reference to any object) • The interpreter determines the type of a particular occurrence of a variable • complication • Variables can be either implicitly or explicitly declared var sum = 0, today = "Monday", flag = false; JS

  17. Primitives, Operations, & Expressions • Number, String, and Boolean have wrapper objects (Number, String, and Boolean) • All numeric values are stored in double-precision floating point • String literals are delimited by either ' or “ • Can include escape sequences (e.g., \t) • Boolean values are true and false • The only Null value is null • The only Undefined value is undefined • In the cases of Number and String, primitive values and objects are coerced back and forth so that primitive values can be treated essentially as if they were objects • Var num_v=Number(str_v); • Var str_v=String(num_v); • Var str_v=num_v.toString(); str_v=num_v.toString(2); JS

  18. Primitives, Operations, & Expressions • Numeric operators - ++, --, +, -, *, /, % • All operations are in double precision A++ - A=A+1; A++ vs ++A; Example • The Math Object • Provides floor, round, max, min, trig functions, etc. • e.g., Math.cos(x) Example Math functions supported by JS http://www.javascripter.net/faq/mathfunc.htm JS

  19. Primitives, Operations, & Expressions • The Number Object Example • Some useful properties: • MAX_VALUE, MIN_VALUE, NaN, POSITIVE_INFINITY, NEGATIVE_INFINITY, PI • e.g., Number.MAX_VALUE • An arithmetic operation that creates overflow returns NaN • NaN is not == to any number, not even itself • Test for it with isNaN(x) • Number object has several methods • toString toFixed toExponential toPrecision valueOf JS

  20. Primitives, Operations, & Expressions • String catenation operator: + - Example • Coercions • Catenation coerces numbers to strings • Numeric operators (other than +) coerce strings to numbers (if either operand of + is a string, it is assumed to be catenation • Conversions from strings to numbers that do not work return NaN • Explicit conversions • Use the String and Number constructors • Use toString method of numbers • Use parseInt and parseFloat on strings • String properties & methods • length e.g., var len = str1.length; (a property) • charAt(position) e.g., str.charAt(3) • indexOf(string) e.g., str.indexOf('B') • substring(from, to) e.g., str.substring(1, 3) • toLowerCase() e.g., str.toLowerCase() JS

  21. Primitives, Operations, & Expressions • The typeof operator Example • Returns "number", "string", or "boolean" for primitives; returns "object" for objects and null • The Data Object • Create one with the Date constructor (no params) • Local time methods of Date: • toLocaleString – returns a string of the date • getDate – returns the day of the month • getMonth – returns the month of the year (0 – 11) • getDay – returns the day of the week (0 – 6) • getFullYear – returns the year • getTime – returns the number of milliseconds since January 1, 1970 • getHours – returns the hour (0 – 23) • getMinutes – returns the minutes (0 – 59) • getMilliseconds – returns the millisecond (0 – 999) Example JS

  22. JS • Introduction • General Syntactic Characteristics • JS write to the XHTML document • Write vs Writeln • Typical JS dialogs • Primitives, Operations, & Expressions • Primitives: Number, String, Boolean, Undefined, Null • Numeric operators • String catenation • Coercions • Control Statements • Selection statements • Loop statements JS

  23. Control Statements • Compound statements are delimited by braces, but compound statements are not blocks • NO local variables • Control expressions – three kinds • Primitive values Example • If it is a string, it is true unless it is empty or "0" • If it is a number, it is true unless it is zero • Relational Expressions Example • ==, !=, <, >, <=, >= • Operands are coerced if necessary (ASCII) • string vs number, it attempts to convert the string to a number • Boolean vs non-boolean, the Boolean operand is coerced to a number (1 or 0) • Compound Expressions • && || ! Example JS

  24. Selection Statements • The usual if-then-else (clauses can be either single statements or compound statements) • Switch switch (expression) { case value_1: // value_1 statements case value_2: // value_2 statements … [default: // default statements] } • The statements can be either statement sequences or compound statements • The control expression can be a number, a string, or a Boolean • Different cases can have values of different types ExampleMoreComplex Example JS

  25. Loop Statements • for (init; control; increment) { statement or cmpnd ExampleContinue } • while (control_expression) Example { statement or cmpnd } • do { Example statement or compound }while (control_expression) JS

  26. JS

  27. JS • Introduction • General Syntactic Characteristics • JS write to the XHTML document • Write vs Writeln • Typical JS dialogs • Primitives, Operations, & Expressions • Primitives: Number, String, Boolean, Undefined, Null • Numeric operators • String catenation • Coercions • Control Statements • Selection statements • Loop statements JS

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