testvar[1] is the value of that array index, which is the number 2. Numbers don't have a length property, and you're checking for 2.length which is undefined. If you want the length of the array just check testvar.length

Mar 2, 2015 · Determining the length of an array is a fundamental operation in JavaScript. We will explore multiple approaches to find the length of an array. Please refer WebDevLearners for more details. Approach 1. Using length Property The most straightforward and commonly used method to find the length of an array is by accessing its length property ...

Jan 24, 2016 · The necessary steps to be fulfilled when length is being set on an Array is described on section 9.4.2.4 ArraySetLength of ES 6.0 language specification. It deletes index properties from the old length of the array to the new length of the array according to step 19: While newLen < oldLen repeat, Set oldLen to oldLen – 1.

May 25, 2017 · we can you use .length property to set or returns number of elements in an array. return value is a number > set the length: let count = myArray.length; > return lengthof an array : myArray.length we can you .size in case we need to filter duplicate values and get the count of elements in a set.

Mar 6, 2012 · To add more about length being a property and not a function, the ECMAScript 2015 Language specification describes Array.length as "a data property whose value is always numerically greater than the name of every configurable own property whose name is …

Jan 31, 2011 · When you call Array.apply with an array or an object with a length property Array is going to use the length to explicitly set each value of the new array. This is why Array(5) gives an array of 5 elisions, while Array.apply(null, Array(5)) gives an array of 5 undefined's.

First one is like fake javascript array (which has property length). When Array.from gets a value of property length (5 in this case), then it creates a real array with length 5. This kind of fakeArray object is often called arrayLike. The second part is just an arrow function which populates an array with values of indices (second argument).

Dec 14, 2011 · The array.slice() method can extract a slice from the beginning, middle, or end of an array for whatever purposes you require, without changing the original array.

Mar 24, 2010 · Yes, variable-length arrays are possible with Javascript's Array prototype. As SLaks noted, you can use .push() and .pop() to add and remove items from the end of the array respectively and the array's length property will increase and decrease by 1 …

Jun 10, 2010 · A note on sparse arrays: an array in JavaScript may not actually store as many items as reported by its length; that number is simply one greater than the highest index at which a value is stored. If the array holds fewer elements …