js uses an array to determine whether the same data exists in the submitted data_javascript skills

Method: 1. Use shift() to delete the first element, the syntax is "array.shift()"; 2. Use pop() to delete the last element, the syntax is "array.pop()"; 3. Use splice() to delete Elements at any position, the syntax is "array.splice(position, number)"; 4. Use length to delete the last N elements, the syntax is "array.length=original array length-N"; 5. Directly assign the empty array "[ ]" to clear the element; 6. Use delete to delete an element at the specified subscript.

3 conversion methods: 1. Use split() to split a given string into a string array, the syntax is "str.split (separator, maximum length of array)"; 2. Use the expansion operator "... ", iterable string object, convert it into a character array, the syntax "[...str]"; 3. Use Array.from() to convert the string into an array, the syntax "Array.from(str) ".

The js array can be converted into a php array. The operation method is: 1. Create a php sample file; 2. Use the syntax "JSON.stringify()" to convert the js array into a string in JSON format; 3. Use the syntax "json_decode()" "Convert the JSON format string to a PHP array. The parameter true is added here, which means that the JSON format string is converted into a PHP associative array.

Getting the length of an array in JS is very simple. Each array has a length property, which returns the maximum length of the array, that is, its value is equal to the maximum subscript value plus 1. Since numeric subscripts must be less than 2^32-1, the maximum value of the length attribute is equal to 2^32-1. The following code defines an empty array, and then assigns a value to the element with the index equal to 100, then the length property returns 101. Therefore, the length attribute cannot reflect the actual number of array elements.

There are 4 ways to delete an element from a js array, namely: 1. Use splice; 2. Use filter; 3. Use the pop method and shift; 4. Use the delete keyword.

JavaScript's Array.prototype.sort() method is used to sort the elements of an array. This method sorts in place, that is, it modifies the original array rather than returning a new sorted array. By default, the sort() method sorts strings according to their Unicode code point values. This means that it is used primarily for sorting strings and numbers, rather than for sorting objects or other complex data types.

Methods to deduplicate js arrays include using Set, using indexOf, using includes, using filter and using reduce. 1. Use Set, which is characterized by the fact that the elements in the set will not be repeated; 2. Use indexOf to return the first index position of the specified element in the array; 3. Use includes to determine whether an element already exists in the array. 4. Use filter to filter elements; 5. Use reduce to compress elements in an array, etc.

In JavaScript, you can use the length attribute to get the length of the array, the syntax is "array object.length"; you can use the reduce() or reduceRight() function to find the sum of elements, the syntax is "arr.reduce(function f(pre,curr){ return pre+cur})" or "arr.reduceRight(function f(pre,curr){return pre+cur})".