Uncaught TypeError: Cannot read property ‘length’ of undefined
You are not passing the variable correctly. One fast solution is to make a global variable like this:
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What’s the best way to convert a number to a string in JavaScript?
like this: Actually, even though I typically do it like this for simple convenience, over 1,000s of iterations it appears for raw speed there is an advantage for .toString() See Performance tests here (not by me, but found when I went to write my own): http://jsben.ch/#/ghQYR Fastest based on the JSPerf test above: str = num.toString(); It should be … Read more
What does this symbol mean in JavaScript?
See the documentation on MDN about expressions and operators and statements. Basic keywords and general expressions this keyword: How does the “this” keyword work? var x = function() vs. function x() — Function declaration syntax var functionName = function() {} vs function functionName() {} (function(){…})() — IIFE (Immediately Invoked Function Expression) What is the purpose?, How is it called? Why does (function(){…})(); work but function(){…}(); doesn’t? (function(){…})(); vs (function(){…}()); shorter alternatives: !function(){…}(); – What … Read more
How to find the sum of an array of numbers
Recommended (reduce with default value) Array.prototype.reduce can be used to iterate through the array, adding the current element value to the sum of the previous element values. Run code snippetExpand snippet Without default value You get a TypeError Run code snippetExpand snippet Prior to ES6’s arrow functions Run code snippetExpand snippet Non-number inputs If non-numbers are … Read more
Nested JSON objects – do I have to use arrays for everything?
You don’t need to use arrays. JSON values can be arrays, objects, or primitives (numbers or strings). You can write JSON like this: You can use it like this:
Setting “checked” for a checkbox with jQuery
Modern jQuery Use .prop(): DOM API If you’re working with just one element, you can always just access the underlying HTMLInputElement and modify its .checked property: The benefit to using the .prop() and .attr() methods instead of this is that they will operate on all matched elements. jQuery 1.5.x and below The .prop() method is not available, so you need to use .attr(). Note that this is the … Read more
After $npm install, Getting Error: Cannot find module ‘../lib/utils/unsupported.js’
Uninstall node brew uninstall –force node Remove the /usr/local/lib/node_modules folder Install it again brew install node
JavaScript “Uncaught TypeError: object is not a function” associativity question
JavaScript does require semicolons. It’s just that the interpreter will insert them for you on line breaks where possible*. Unfortunately, the code does not result in a syntax error, so no ; will be inserted. (An example which can run is To avoid surprises like this, train yourself to always end a statement with ;. * This is just a rule … Read more
‘react-scripts’ is not recognized as an internal or external command
I’ve got a maven project, within which is JavaScript project cloned as a git sub-module. So the directory structure looks like mavenapp/src/main/javascript/[npm project files] Inside my package.json, the test looks like this: but when I try to run npm test, it says ‘react-scripts’ is not recognized as an internal or external command, Interestingly, when I clone the … Read more
Check if a variable is a string in JavaScript
You can use typeof operator: Example from this webpage. (Example was slightly modified though). This won’t work as expected in the case of strings created with new String(), but this is seldom used and recommended against[1][2]. See the other answers for how to handle these, if you so desire. The Google JavaScript Style Guide says to never use primitive object … Read more