So, our array of four elements has indexes from 0 to 3. As we can see data is an object, hence we can access its properties using dot notation. JavaScript arrays are zero based, which means the first item is referenced with an index of 0. The items property is accessed as follows: data.items The value is an array, to access its second element, we have to use bracket notation: data.items[1] This value is an object and we use dot notation again to access the name property. Here is an example that demonstrates $.ajax() and shows you how to access the returned values in an array. We can loop through the entirety of the array with the for keyword, taking advantage of the length property. It would help to know what your AJAX request looks like. The following example illustrates this behavior. The problem most likely is that the value is undefined at some point in the components lifecycle (you're probably loading it asynchronously). The Basic For Loop. I ask because when you find yourself trying to circumvent one of the most basic characteristics of a programming language, odds are good there's a better way to do what you're trying to do. I want to create an array whose indexing starts from 1 instead. JavaScript for loops iterate over each item in an array. – Strille Oct 3 '13 at 9:04 As we saw, arrays can have several dimensions, which means that an array element can contain an array, whose elements can contain arrays, etc. I recommend using $.ajax() and specifying the dataType as JSON, or using $.getJSON(). In the above example, we removed seahorse from the array, and pushed a new value into index 3. An “indexed” array is one where the index must be an integer, and you access its elements using its index as a reference. This means that array indexes start at 0 and go up to the number of elements, minus 1. let arr = Array (9.3) // RangeError: Invalid array length. It sounds like the data structure is confusing :-) If you have an object with unknown/random property names, you can't really access a specific property without knowing the name. You are going to need be be defensive in the way that you reference your property. Calling Array(N) results in a RangeError, if N is a non-whole number whose fractional portion is non-zero. Looping Through an Array. It's not like an array where you can access a value by index ("pick the first value"). Here’s an example of an indexed array: Here’s an example of … Referencing items in arrays is done with a numeric index, starting at zero and ending with the array length minus 1. By default the indexing of every JavaScript array starts from 0. An array can hold many values under a single name, and you can access the values by referring to an index number. The syntax to access an array member Remember that the index values start at 0, not 1. 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