{"id":4346,"date":"2022-04-12T10:32:14","date_gmt":"2022-04-12T10:32:14","guid":{"rendered":"http:\/\/truelogic.org\/wordpress\/?p=4346"},"modified":"2022-04-12T10:32:15","modified_gmt":"2022-04-12T10:32:15","slug":"javascript-promises","status":"publish","type":"post","link":"https:\/\/truelogic.org\/wordpress\/2022\/04\/12\/javascript-promises\/","title":{"rendered":"Javascript – Promises"},"content":{"rendered":"\n

OVERVIEW<\/strong><\/p>\n\n\n\n

Promises are a way of handling asynchronous events in javascript. Prior to promises, the only true asynchronous feature was in XMLHttpRequest<\/em> where ajax calls were made. <\/p>\n\n\n\n

A Promise is an object whose constructor takes in an anonymous function. The anonymous function has two arguments – resolve and reject. When the code within the anonymous functions finishes, it can either call resolve or reject . Resolve means it was successful and Reject means that some problem or error occurred.<\/p>\n\n\n\n

The constructor defines the actual processing code and the calls to resolve and reject. The handling of the resolve and reject callback functions are done using the then<\/em> and catch <\/em>method of the Promise object. The then <\/em>method will be called if resolve<\/em> was executed. The catch method will be called if reject<\/em> was executed.<\/p>\n\n\n\n

The sample source is given below:<\/p>\n\n\n

\n<html>\n\t<head>\n\t\t\n\t\t<title>Javascript Promises<\/title>\n\t\n\t  <script>\n\n\t\n\t\tfunction doIt() {\n\t\t        var promise = new Promise(function(resolve, reject) {\n\t\t\t  var x = Math.floor(Math.random()*10);\t\n\t\t\t  if (x % 2 == 0)\n\t\t\t\t  resolve(x);\n\t\t\t  else\n\t\t\t\t  reject(x);\n\t\t  });\n\n\t\t  promise.then(function(x) {\n\t\t  \talert(x + " was even");\n\t\t  }).catch(function(x) {\n\t\t\talert( x + " was not even");\t\t  \n\t\t  });\n\n\t\t}\n\t  <\/script>\n\t<\/head>\n\n\t<body>\n\n\t\t<button type=button onclick="doIt(); return false;">Click Me<\/button>\n\t<\/body>\n<\/html>\n\n<\/pre><\/div>\n\n\n
Depending on whether the random number is even or odd, the relevant alert will show. <\/p>\n\n\n\n
<\/p>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
OVERVIEW Promises are a way of handling asynchronous events in javascript. Prior to promises, the only true asynchronous feature was in XMLHttpRequest where ajax calls […]<\/a><\/p>\n<\/div>","protected":false},"author":1,"featured_media":2463,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[18],"tags":[],"class_list":["post-4346","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-javascript"],"_links":{"self":[{"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/posts\/4346","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/comments?post=4346"}],"version-history":[{"count":1,"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/posts\/4346\/revisions"}],"predecessor-version":[{"id":4347,"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/posts\/4346\/revisions\/4347"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/media\/2463"}],"wp:attachment":[{"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/media?parent=4346"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/categories?post=4346"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/truelogic.org\/wordpress\/wp-json\/wp\/v2\/tags?post=4346"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}