Add your <script> to the bottom of your <body>, or add an event listener for DOMContentLoaded following this StackOverflow question. If that script executes in the <head> section of the code, document.getElementsByClassName(…) will return an empty array because the DOM is not loaded yet. You’re getting the Type Error because you’re referencing search_span[0], but search_span[0] … Read more
Objects There is no benefit to using new Object(); – whereas {}; can make your code more compact, and more readable. For defining empty objects they’re technically the same. The {} syntax is shorter, neater (less Java-ish), and allows you to instantly populate the object inline – like so: Arrays For arrays, there’s similarly almost no benefit to ever using new Array(); over []; – … Read more
Updated answer Here’s an update as of 2016 and widespread deployment of ES5 and beyond. For IE9+ and all other modern ES5+ capable browsers, you can use Object.keys() so the above code just becomes: This doesn’t have to modify any existing prototype since Object.keys() is now built-in. Edit: Objects can have symbolic properties that can not be returned via Object.key method. So … Read more
If you want to print the object for debugging purposes, use the code: will display: Note: you must only log the object. For example, this won’t work: Note ‘: You can also use a comma in the log method, then the first line of the output will be the string and after that, the object will be rendered:
UPDATE: This answer is incomplete and gives misleading results. For example, null is also considered of type object in JavaScript, not to mention several other edge cases. Follow the recommendation below and move on to other “most upvoted (and correct!) answer”: Original answer: Try using typeof(var) and/or var instanceof something. EDIT: This answer gives an idea of how to examine variable’s properties, but … Read more
If you want to print the object for debugging purposes, use the code: will display: Note: you must only log the object. For example, this won’t work: Note ‘: You can also use a comma in the log method, then the first line of the output will be the string and after that, the object will be rendered:
To do this for any object in JavaScript will not be simple or straightforward. You will run into the problem of erroneously picking up attributes from the object’s prototype that should be left in the prototype and not copied to the new instance. If, for instance, you are adding a clone method to Object.prototype, as some answers depict, … Read more
For most objects, use for .. in : With ES6, if you need both keys and values simultaneously, do To avoid logging inherited properties, check with hasOwnProperty : You don’t need to check hasOwnProperty when iterating on keys if you’re using a simple object (for example one you made yourself with {}). This MDN documentation explains more generally how to deal with objects … Read more
ECMA 5+: Note, though, that this creates an unnecessary array (the return value of keys). Pre-ECMA 5: jQuery: lodash: Underscore: Hoek ExtJS AngularJS (version 1) Ramda
ECMAScript 2018 Standard Method You would use object spread: merged is now the union of obj1 and obj2. Properties in obj2 will overwrite those in obj1. Here is also the MDN documentation for this syntax. If you’re using babel you’ll need the babel-plugin-transform-object-rest-spread plugin for it to work. ECMAScript 2015 (ES6) Standard Method Method for ES5 and Earlier Note that this will simply add all attributes of obj2 to obj1 which … Read more