{"id":65784,"date":"2021-07-14T04:10:05","date_gmt":"2021-07-14T08:10:05","guid":{"rendered":"http:\/\/bangla.salearningschool.com\/recent-posts\/some-javascript-stuff-that-you-need-to-know-javascript\/"},"modified":"2021-07-14T04:10:05","modified_gmt":"2021-07-14T08:10:05","slug":"some-javascript-stuff-that-you-need-to-know-javascript","status":"publish","type":"post","link":"http:\/\/bangla.sitestree.com\/?p=65784","title":{"rendered":"Some JavaScript stuff that you need to know #JavaScript"},"content":{"rendered":"
What you really need to learn in Javascript? \r\n\t\t\t\t\t\t\t\t\r\n\t\t\t\t\t\t\t\t\t\t\r\n\r\n1. Where you can place JavaScript codes? \r\n\r\nAnywhere in the web-pages, ideally in the header section, or in an external file. If you keep \r\njavascript\r\n codes in an external file, the codes will be re-usable from different web-pages\r\n\r\n2. Some basic programming: \r\n<script language=\"javascript\" type=\"text\/javascript\">\r\n<\/script> \r\n\r\n\r\n<script language=\"javascript\" type=\"text\/javascript\"> \r\n\tdocument.write('<b>Hello World<\/b>'); \r\n<\/script> \r\n\r\nThis will only be displayed in javascript enabled browsers.\r\n\r\n<script language=\"javascript\" type=\"text\/javascript\"> \r\n\tdocument.write('<a href=\"script.htm\">Page Requiring Javascript<\/a>'); \r\n<\/script> \r\n\r\n3. Variables and their scopes \r\n\r\n<script language=\"javascript\" type=\"text\/javascript\"> \r\n\tvar hello = 'Hello World'; \r\n\tdocument.write(hello);\r\n<\/script> \r\n\r\n\r\nvar mynum = 5; \r\nvar smokes = false; \r\nvar riches = null; \r\nvar today = new Date;\r\n \r\nExample use of variables: \r\n<script language=\"javascript\" type=\"text\/javascript\"> \r\n\tvar questions = '<p>If you have any questions about this \r\n \tplease <a href=\"mailto:me@myaddress.com\">email me<\/a>.<\/p>'; \r\n\tdocument.write(questions);\r\n<\/script> \r\n\r\nAnother block can refer to questions variables without reassigning the value\r\n\r\n<script language=\"javascript\" type=\"text\/javascript\"> \r\n\tdocument.write(questions);\r\n<\/script> \r\n\r\n\r\nvariables declared within a function is recognized only withing that function. Variables \r\ndeclared \r\noutside of a \r\nfunction is recognized anywhere in the webpage within javascript code from the declaration \r\nplace.\r\n \r\n\r\n\r\n4. Operators \r\n\r\nAssignment operators \r\n\r\n<script language=\"javascript\" type=\"text\/javascript\"> \r\n\tvar rich = 5000; \r\n\tvar lotsOfMoney = 100000; \r\n\trich = lotsOfMoney; \r\n\tdocument.write(rich);\r\n<\/script> \r\n\r\nArithmetic and concatenation operators \r\n\r\nfive = two + three; \r\nprofit = income - expenses; \r\nincome = sales * price;\r\npayment = total \/ instalments; \r\noption = randnum % choices; \r\nb = ++a;\r\nc = a++;\r\nd = --a;\r\ne = a--; \r\n\r\n\r\nCombination of Operators like c\/c++ \r\n\r\njoy += happiness; \r\nprice -= discount; \r\ncapital *= interest; \r\npie \/= slices;\r\noptions %= choice; \r\n\r\nExample use:\r\n\r\n\r\n<script language=\"javascript\" type=\"text\/javascript\"> \r\n\tvar singlePrice = 8;\r\n\tvar bulkPrice = singlePrice * 9;\r\n\tdocument.write('<p>Buy our Widgets $'\r\n\t+singlePrice+' for one, $'+bulkPrice+' for ten<\/p>'); \r\n<\/script> \r\n\r\n\r\n\r\n5. Comparing Variables, Logical statements \r\n\r\n<script language=\"javascript\" type=\"text\/javascript\"> \r\n\tvar red = 5;\r\n\tvar blue = 3;\r\n\tvar match = null;\r\n\tif (red == blue) \r\n\t{\r\n\t\tmatch = 'equal'; \r\n\t} \r\n\telse \r\n\t{\r\n\t\tmatch = 'unequal'; \r\n\t}\r\n\tdocument.write(red + ' and ' + blue + ' are ' + match); \r\n<\/script> \r\n\r\n\r\nOther comparison operators: \r\n\r\nif (red > blue)\r\nif (red >= blue)\r\nif (red < blue)\r\nif (red <= blue)\r\nif (red != blue) \r\n\r\n\r\n\r\nCombining more than one comparison \r\n\r\nif ((red == blue) || (red == green)) \r\n\r\n\r\n<script language=\"javascript\" type=\"text\/javascript\"> \r\n\tvar red = 5;\r\n\tvar blue = 3;\r\n\tvar green = 3;\r\n\tvar match = null;\r\n\t\r\n\tif ((red == blue) && (red == green)) \r\n\t{\r\n\t\tmatch = 'equal';\r\n\t} \r\n\telse \r\n\t{\r\n\t\tpurple = 'unequal';\r\n\t}\r\n\tdocument.write(red + ' and ' + blue + ' are ' + match);\r\n<\/script> \r\n\r\n\r\nComparison in short\r\n\r\nred == blue ? match = 'equal' : match = 'unequal'; \r\n\r\n\r\ninstead of\r\n\r\nif (red == blue) \r\n{\r\n\tmatch = 'equal';\r\n} \r\nelse \r\n{\r\n      match = 'unequal'; \r\n}\r\n\r\n\r\nExample Use:\r\n\r\n<script language=\"javascript\" type=\"text\/javascript\">\r\n\tvar discPrice = 25;\r\n\tvar regPrice = 25;\r\n\tvar discount = regPrice - discPrice;\r\n\tif (discount > 0)\r\n\t\tdocument.write('<p>Save $'+discount+ ' off the normal price of $' +regPrice+ 'now only \r\n$'+discPrice+'.<\/p>');\r\n\telse\r\n\t\tdocument.write('<p>Buy now at our regular cheap price of $' + \r\nregPrice+'.<\/p>' ); \r\n<\/script>\r\n\r\n\r\n6. Switch statement in Javascript, very similar to C\/C++\/Java\r\n\r\nuse switch instead of multiple if\/else if\r\n\r\n<script language=\"javascript\" type=\"text\/javascript\">\r\n\tvar red = 1;\r\n\tvar result = null;\r\n\tswitch (red) \r\n\t{\r\n\t\tcase 1: result = 'one'; break; \r\n\t\tcase 2: result = 'two'; break;\r\n\t\tdefault: result = 'unknown';\r\n\t}\r\n\tdocument.write(result);\r\n<\/script> \r\n\r\n\r\nExample:\r\n\r\n<script language=\"javascript\" type=\"text\/javascript\"> \r\n\tvar message = 0;\r\n\tswitch (message) \r\n\t{\r\n\t\tcase 1: document.write('Merry Christmas'); break;\r\n\t\tcase 2: document.write('Happy New Year'); break; \r\n\t\tcase 3: document.write('Happy Easter'); break;\r\n\t\tcase 4: document.write('Happy Holidays'); break;\r\n\t\tdefault: document.write('Welcome');\r\n\t}\r\n<\/script> \r\n\r\n\r\n7. Function \r\n\t\r\n\t\r\nDefining a function \r\n\r\nfunction myCode() \r\n{\r\n\tdocument.write('<b>Hello World<\/b>'); \r\n} \r\n\r\ncalling a function\r\n\r\nmyCode()\r\n\r\nExample:\r\n\r\nfunction displayMessage() \r\n{\r\n\tswitch (message) \r\n\t{\r\n\t\tcase 1: document.write('Merry Christmas'); break;\r\n\t\tcase 2: document.write('Happy New Year'); break;\r\n\t\tcase 3: document.write('Happy Easter'); break;\r\n\t\tcase 4: document.write('Happy Holidays'); break;\r\n\t\tdefault: document.write('Welcome');\r\n\t}\r\n}\t \r\n\r\n\r\nvar message = 0;\r\ndisplayMessage(); \r\n\r\n\r\nparameter passing\r\n\r\nfunction writeSentence(argument1,argument2) \r\n{\r\n\tdocument.write('The '+argument1+' is '+argument2+'.<br \/>'); \r\n} \r\n\r\n\r\n\r\nvar a = 'table';\r\nvar b = 'chair';\r\nvar c = 'red';\r\nvar d = 'blue';\r\nwriteSentence(a,c);\r\nwriteSentence(b,c);\r\nb = 'other ' + b;\r\nwriteSentence(b,d); \r\nwriteSentence('table',b); \/\/passing the value directly\r\n\r\nExample:\r\n\r\nfunction displayMessage(m) \r\n{\r\n\tswitch (m) \r\n\t{\r\n\t\tcase 1: document.write('Merry Christmas'); break;\r\n\t\tcase 2: document.write('Happy New Year'); break;\r\n\t\tcase 3: document.write('Happy Easter'); break;\r\n\t\tcase 4: document.write('Happy Holidays'); break;\r\n\t\tdefault: document.write('Welcome');\r\n\t}\r\n} \r\n\r\n\r\nIn Javascript functions can also return values \r\n\r\nfunction validField(fld) \r\n{\r\n\tif (fld == '') return false; \r\n\treturn true;\r\n} \r\n\r\n\r\nfunction validField(fld) \r\n{\r\n\treturn (fld != '');\r\n} \r\n\r\nHow to receive returned values and process \r\ndocument.write(myField + ' is ');\r\nif (!validField(myField)) \r\n{\r\n\tdocument.write('not '); \r\n}\r\ndocument.write('empty'); \r\n\r\n8. Alert and confirm \r\n\r\n\t\r\nalert('Alert Message');  \r\n\r\nWill display a message box with the message. Very useful in debugging javascript applications. \r\n\r\n\r\nuse confirm(), when you need user agreement on an issue. like: \r\n\r\nif (confirm('Select a button'))\r\n{\r\n\talert('You selected OK'); \r\n}\r\nelse \r\n{\r\n\talert('You selected Cancel'); \r\n}\r\n\r\n\r\n9. comments \r\n\r\n\r\n\/\/ Scrolling Ad Javascript\r\n\/\/ copyright 3rd September 2004, by Stephen Chapman \r\n\/\/ permission to use this Javascript on your web page is \r\n\/\/ granted provided that all of the code in this script (including \r\n\/\/ these comments) is used without any alteration \r\n\r\n\r\nor\r\n\r\n\r\n\/* Scrolling Ad Javascript\r\ncopyright 3rd September 2004, by Stephen Chapman\r\npermission to use this Javascript on your web page is\r\ngranted provided that all of the code in this script (including\r\nthese comments) is used without any alteration *\/ \r\n\r\n\r\n\r\n10. Debugging JavaScript\r\n\r\n    Test in different browsers like IE, Mozilla, Firfox, Netscape \r\n    Enable Javascript and script debugging\r\n    Script debugging usually reside under tools menu under browsing or web development \r\nsub-options\r\n\r\n    \r\n    \r\n    Using alert to check variable values or if you can reach to a particular point of your \r\ncode\r\n    \r\n    use bookmarklets, these are small scripts that can be used as plug in into browsers to \r\nprovide error information.\r\n    \r\n    \r\n    Use firebug in firefox, also use error console under tools menu to debug javascript\r\n error.\r\n    \r\n    Visual interdev provides Javascript debugging you may also enable external debugging by \r\nsuch programs\r\n    \r\n    \r\n11. External javascript\r\n\r\n\r\nYou can place all of your javascript codes to an external file. and use the file \r\nscripts\/functions from any webpage. \r\nYou just need to provide a reference to that external file.\r\n\r\nYou can provide reference as follows:\r\n\r\nhttp:\/\/hello.js<\/a> \r\n\r\nNote:  do not include any <script> or <\/script> in the external file. \r\n\r\n\r\n12.  Using <noscript> tag:  this tag may help you to provide some information to the\r\n visitors  \r\nwhen javascript is disabled or not supported by the browsers.\r\n\r\n\r\n<script language=\"javascript\" type=\"text\/javascript\">\r\n\tdocument.write('<b>Hello Javascript World<\/b>'); \r\n<\/script>\r\n\r\n<noscript>Hello World Without Javascript<\/noscript> \r\n\r\n<noscript>\r\n\tThis page uses Javascript. Your browser either\r\n\tdoesn't support Javascript or you have it turned off.\r\n\tTo see this page as it is meant to appear please use\r\n\ta Javascript enabled browser.\r\n<\/noscript>\r\n\r\n\r\n13. Objects and properties in Javascript \r\n\r\nvar strlen = myField.length; \r\nvar str = mynum.toString(); \r\n\r\nfunction theLetter(num) \r\n{\r\n\tvar str = 'abcdefghijklmnopqustuvwxyz';\r\n\treturn str.substr(num-1,1);\r\n}\r\n\r\ndocument.write(theLetter(5)); \r\n\r\n\r\n14. Arrays in Javascript \r\n\r\nvar myArray = new Array(); \r\n\r\nvar myArray = new Array('message one',\r\n'message two','message three'); \r\ndocument.write(myArray[0]); \r\nmyArray[3] = 'message four'; \r\n\r\n\r\nfunction displayMessage(m) \r\n{\r\n\tvar greeting = new Array('Welcome','Merry Christmas',\r\n\t'Happy New Year','Happy Easter','Happy Holidays');\r\n\tif (m < 0 || m > greeting.length) m = 0;\r\n\tdocument.write(greeting[m]); \r\n\r\n} \r\n\r\n15. Loops\r\n\r\nfor (var i=0; i<10; i++) \r\n{\r\n\tdocument.write(i);\r\n} \r\n\r\n\r\nvar x = 0;\r\nwhile (x<10) \r\n{\r\n\tdocument.write(x); \r\n\tx++;\r\n} \r\n\r\nvar x = 12;\r\ndo \r\n{\r\n\tdocument.write(x); \r\n\tx++;\r\n} while (x<10) \r\n\r\n\r\n16. Date and Time in Javascript\r\n\r\n\/\/current date\r\nvar myDate = new Date; \r\n\r\n\r\nmyDate.setDate(15);\r\nmyDate.setMonth(3); \/\/ January = 0\r\nmyDate.setFullYear(2006); \r\n\r\nmyDate.setDate(myDate.getDate()+7);<\/pre>\n
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What you really need to learn in Javascript? 1. Where you can place JavaScript codes? Anywhere in the web-pages, ideally in the header section, or in an external file. If you keep javascript codes in an external file, the codes will be re-usable from different web-pages 2. Some basic programming: <script language=”javascript” type=”text\/javascript”> <\/script> <script … <\/p>\n
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