This is because we defined an array of Strings, not Integers. However, be aware that indexOf() uses the strict comparison operator (=), so the following will not work:Ĭonsole.log(arr.indexOf(2)) // returns -1 For example, to check whether a particular value is present in an array: The indexOf() and lastIndexOf() functions are very useful for searching an array for a particular value, if necessary. Returns the last (greatest) index of an element within the array equal to the specified value, or -1 if none is found.The array is searched backwards, starting at fromIndex. The search can optionally begin at fromIndex. Returns the first (least) index of an element within the array equal to the specified value, or -1 if none is found. Returns true if a variable is an array, false if it is not. Objects can also be useful for values which need to be looked up quickly, since you can simply check for whether a property is defined without needing to iterate through the properties:Īrrays are very versatile for storing data, and can be searched, tested, and have functions applied to them in V8 using the following ECMAScript 5 functions: Searching the content of an Array Array.isArray(array) Objects are good for storing named values, but V8 does not allow you to specify an order for the properties (so adding properties in a particular order to an object does not guarantee that the properties will be iterated in that order). Hence, you should use arrays for storing items which are ordered. Unshift() and shift() work on the front of the array:Īrr.unshift('1') // insert as first itemĬonsole.log(arr.shift()) // remove first itemĪrrays are ordered - the order in which you add items (e.g. Arrays can also be used as stacks:Ĭonsole.log(arr) // Ĭonsole.log(arr.pop()) // remove last item You have the choice between using arrays or objects for storing your data in Javascript. Even IE is finally adding support for ECMA 5 - in IE9. The ECMAScript 5 additions make writing server side code nicer. Typically when writing Javascript for execution on the client side you have to force yourself to the lowest common denominator. If you haven't heard of those functions, it's because they are part of ECMAScript 5, which is not supported by Internet Explorer versions prior to IE9. There are a number of useful ECMAScript 5 features which are supported by V8, such as Array.forEach(), Array.indexOf(), Object.keys() and im(). This chapter focuses on Arrays, Objects and Functions. Accepting variable number of arguments in functions.Iterating through the properties (keys) of an object.Checking whether the contents of an Array satisfy a criteria.Mozilla versions dating back to at least 2003) respect this.In this chapter, I go through a number of useful ECMA5 functions for situations such as: Note: the ECMAscript standard does not guarantee this behavior, thus, not all browsers (e.g. So, if compareFunction(a, b) returns 0, leave a and b unchanged with respect to each other, but sorted with respect to all different elements. If the result is 0 no changes are done with the sort order of the two values. In other words, return 0 if a equals b. So, if compareFunction(a, b) returns greater than 0, sort b to an index lower than a (i.e. If the result is positive b is sorted before a. In other words, return greater than 0 if a is greater than b. So, if compareFunction(a, b) returns less than 0, sort a to an index lower than b (i.e. In other words, return less than 0 if a is less than b. If the result is negative a is sorted before b. Then you make the compare function return 0, greater than 0, or less than 0, based on these values, a and b. The “compare” function must take two arguments, often referred to as a and b. When the sort() function compares two values, it sends the values to the compare function, and sorts the values according to the returned (negative, zero, positive) value. The compare function should return a negative, zero, or positive value, depending on the arguments: The purpose of the compare function is to define an alternative sort order.
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