How to find the sum of an array using JavaScript

Method: 1. Use the statement "arr.reduce(function f(pre,curr){return pre cur})"; 2. Use "arr.reduceRight(function f(pre,curr){return pre cur})".

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

Find the sum of an array using JavaScript

Method 1: Use reduce()

reduce () Computes array elements into a value (from left to right).

var a = [1, 2, 3, 4, 5];
var b =a.reduce(function f(pre, curr){
	return pre + curr;
	});
console.log(b);

Description: The

reduce() method can call the specified callback function for all elements in the array. The return value of this callback function is the cumulative result, and this return value is provided as a parameter the next time the callback function is called. The specific usage is as follows:

array.reduce(callbackfn[, initialVaule]);

Parameter description:

• array: required parameter, an array object.

• callbackfn: required parameter, a function that accepts up to four parameters. The recover() method calls the callbackfn function once for each element in the array.

• initialVaule: Optional parameter, if initialVaule is specified, it will be used as the initial value to start accumulation. The first call to the callbackfn function supplies this value as a parameter instead of an array value.

The return value of the reduce() method is the cumulative result obtained by the last call to the callback function.

If the parameter initialVaule is provided, the reduce() method will call the callbackfn function once for each element in the array (in ascending index order); if the initialVaule is not provided, the reduce() method will call the callbackfn function once for each element in the array. The callbackfn function is called for each element starting with 2 elements.

The return value of the callback function is provided as the previousValue parameter the next time the callback function is called. The return value obtained from the last call to the callback function is the return value of the recude() method. This method does not call the callback function for missing elements in the array.

The syntax of the callback function is as follows:

function callbackfn(previousValue, currentVaule, currentIndex, array);

Description of callback function parameters:

• PreviousValue: The value obtained by the last call to the callback function. If initialValue is provided to the reduce() method, the previousValue is initialValue when the function is first called.

• currentValue: The value of the current element array.

• currentIndex: The numeric index of the current array element.

• array: Array object containing the element.

When the callback function is first called, the value provided as a parameter depends on whether the reduce() method has an initialValue parameter. If initialValue is provided to the recude() method, the previousValue parameter is the initialValue and the currentValue parameter is the value of the 1st element in the array.

Method 2: Use reduceRight()

reduceRight() to calculate the array elements into a value (from right to left).

var arr = [1, 2, 3, 4, 5, 5];
var b =arr.reduceRight(function f(pre, curr){
	return pre + curr;
	});
console.log(b);

Description: The

reduceRight() method can call the specified callback function on all elements in the array from right to left. The return value of this callback function is the cumulative result, and this return value is provided as a parameter the next time the callback function is called. The specific usage is as follows:

array.reduceRight(callbackfn[, initialValue]);

The syntax and usage of this method are roughly the same as the reduce() method. The only difference is that it calls the callback function starting from the right side of the array. If initialValue is provided, the reduceRight() method calls the callbackfn function once for each element in the array in descending index order. If initialValue is not provided, the reduceRight() method calls the callbackfn function on each element in descending index order, starting with the 2nd to last element.

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