{"id":1050,"date":"2019-01-31T13:29:08","date_gmt":"2019-01-31T07:59:08","guid":{"rendered":"http:\/\/blog.openwebsolutions.in\/?p=1050"},"modified":"2019-01-31T13:29:50","modified_gmt":"2019-01-31T07:59:50","slug":"know-perfect-way-error-handling-javascript","status":"publish","type":"post","link":"https:\/\/openwebsolutions.in\/blog\/know-perfect-way-error-handling-javascript\/","title":{"rendered":"Know the perfect way of Error handling in JavaScript"},"content":{"rendered":"

Sometimes a developer is great at programming, but the scripts may have errors. There are various reasons for these errors. Sometimes it occurs because of our mistakes or maybe an unexpected user input, or it could be an erroneous server response and there could be a thousand of other reasons.<\/span><\/p>\n

Generally, a script stops it\u2019s execution after an error occurred, printing it to console.<\/span><\/p>\n

To overcome this there\u2019s a syntax construct try…catch which allows to \u201ccatch\u201d errors and, instead of stopping the execution, do something more reasonable.<\/span><\/p>\n

The \u201ctry\u2026catch\u201d syntax<\/span><\/h2>\n

The try…catch consists of two blocks: try, and then catch<\/span><\/p>\n

try<\/b> {<\/b>
\n<\/b>\/\/ Here is your code…<\/b>
\n<\/b>}<\/b> catch<\/b> (<\/b>err<\/b>)<\/b> {<\/b>
\n<\/b>\u00a0<\/b>\/\/ error handling<\/b>
\n<\/b>}<\/b><\/p>\n

It works like this<\/span><\/h2>\n
    \n
  1. First, the code in <\/span>try{…} block is executed.<\/span><\/li>\n
  2. If there were no errors, then <\/span>catch(err)<\/span> block is ignored and the execution reaches the end of <\/span>try<\/span> and then jumps over <\/span>catch<\/span>.<\/span><\/li>\n
  3. If any error occurred during the execution of the try block, then <\/span>the<\/span> execution is stopped, and the control flows to catch(err)<\/span>. The <\/span>err <\/span>variable contains an error object contains the details of the error…<\/span><\/li>\n<\/ol>\n

    Example:<\/span><\/p>\n

    try {
    \nalert(‘Start of try block’);
    \nabcd; \/\/ error, variable is not defined!
    \nalert(‘End of try’);
    \n} catch(err) {
    \nalert(`Some error has occurred!`);<\/p>\n

    }
    \nalert(“the execution continues”);<\/p>\n

     <\/p>\n

    Things to be remembered<\/span><\/h2>\n

    try..catch<\/b> only works for runtime errors<\/b><\/p>\n

    For <\/span>try..catch<\/span> to work, the code must be valid. i.e., it should be a valid JavaScript.<\/span><\/p>\n

    try..catch<\/b> works synchronously<\/b><\/p>\n

    If any exception happens within a \u00a0\u201cscheduled\u201d code, like <\/span>setTimeout<\/span>, then <\/span>try..catch<\/span> won\u2019t catch the error: That\u2019s because within a setTimeout call the function executed later, when the engine already left the try…catch block. To catch an exception inside a setTimeout function, <\/span>try..catch<\/span> must be inside that function:<\/span><\/p>\n

    Error object<\/span><\/h2>\n

    During the execution, if an error occurred then JavaScript generates an object which contains the details of the error. Then the error object is passed as an argument to <\/span>catch<\/span>:<\/span><\/p>\n

    try {<\/strong>
    \n \u00a0\/\/ …<\/strong>
    \n} catch(err) { \/\/ err is the “error object”, you could use another word instead of err<\/strong>
    \n \u00a0\/\/ …<\/strong>
    \n}<\/strong><\/p>\n

    The error object inside <\/span>catch<\/span> block has two main properties:<\/span><\/p>\n

    Name<\/b><\/p>\n

    Error name. For an undefined variable that\u2019s <\/span>“ReferenceError”<\/span>.<\/span><\/p>\n

    Message<\/b><\/p>\n

    Textual message about error details.<\/span><\/p>\n

    Try\u2026catch\u2026finally<\/h2>\n

    The <\/span>try..catch<\/span> block may have one more code clause: <\/span>finally<\/span>.<\/span><\/p>\n

    If it exists, it runs in all cases:<\/span><\/p>\n

      \n
    • after <\/span>try<\/span>, if there were no errors,<\/span><\/li>\n
    • after <\/span>catch<\/span>, if there were errors.<\/span><\/li>\n<\/ul>\n

      The syntax looks like this:<\/span> \u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>
      \n<\/span>
      \n<\/span>try {
      \ntry to execute the code
      \n} catch(e) {
      \nhandle errors
      \n} finally {
      \nexecute always
      \n}<\/strong><\/p>\n

      The code has two ways of execution:<\/span><\/p>\n

        \n
      • If the code has some error,then <\/span>try -> catch -> finally<\/span>.<\/span><\/li>\n
      • If there were no error, then <\/span>try -> finally<\/span>.<\/span><\/li>\n<\/ul>\n

        Summary<\/span><\/h2>\n

        The <\/span>try..catch<\/span> block allows to handle any runtime errors.<\/span><\/p>\n

        The syntax is:<\/span><\/p>\n

        try {
        \n\/\/ Hereis your code
        \n} catch(err) {
        \n\/\/ if an error happened, then jump here
        \n\/\/ err is the error object
        \n} finally {
        \n\/\/ execute this in any case after try\/catch
        \n}<\/strong><\/p>\n

         <\/p>\n","protected":false},"excerpt":{"rendered":"

        Sometimes a developer is great at programming, but the scripts may have errors. There are various reasons for these errors. Sometimes it occurs because of our mistakes or maybe an unexpected user input, or it could be an erroneous server response and there could be a thousand of other reasons. Generally, a script stops it\u2019s […]<\/p>\n","protected":false},"author":7,"featured_media":1106,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[12,72],"tags":[43,73,15],"yoast_head":"\nKnow the perfect way of Error handling in JavaScript<\/title>\n<meta name=\"robots\" content=\"index, follow\" \/>\n<meta name=\"googlebot\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<meta name=\"bingbot\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/openwebsolutions.in\/blog\/know-perfect-way-error-handling-javascript\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Know the perfect way of Error handling in JavaScript\" \/>\n<meta property=\"og:description\" content=\"Sometimes a developer is great at programming, but the scripts may have errors. 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