Mawaka ya kusaidia ya JavaScript

Hali za kusaidia mawaka zina kufanya hali kwa kila kipimo cha mawaka.

Array.forEach()

forEach() Hali hii inakubadilisha hali kwa kila mawaka katika mawaka (hali ya kurekwa).

实例

var txt = "";
var numbers = [45, 4, 9, 16, 25];
numbers.forEach(myFunction);
function myFunction(value, index, array) {
  txt = txt + value + "<br>"; 
}

亲自试一试

Tsan:Hali hii ina thamani 3:

  • 项目值
  • 项目索引
  • 数组本身

Mfano huu tu tumia thamani za value. Mfano huu inaweza kurekwa tena kama:

实例

var txt = "";
var numbers = [45, 4, 9, 16, 25];
numbers.forEach(myFunction);
function myFunction(value) {
  txt = txt + value + "<br>"; 
}

亲自试一试

Alli kai browsers suka. Array.forEach()，sai kai Internet Explorer 8 tsa bai tsa.

Hai 9.0 Hai Hai Hai

Array.map()

map() Hali hii inakuzalisha mawaka mpya kwa kufanya hali kwa kila mawaka katika mawaka.

map() Hali hii haingaa hali kwa mawaka ya bila thamani.

map() Hali hii haikubadilisha mawaka ya asili.

Mfano huu una kuzalisha kila thamani ya mawaka kwa 2:

实例

var numbers1 = [45, 4, 9, 16, 25];
var numbers2 = numbers1.map(myFunction);
function myFunction(value, index, array) {
  return value * 2;
}

亲自试一试

Raba ina thamani 3:

  • 项目值
  • 项目索引
  • 数组本身

Kama hali ya kurekwa inatumia thamani za value pekee, thamani za index na array inaweza kuwa inasikitika:

实例

var numbers1 = [45, 4, 9, 16, 25];
var numbers2 = numbers1.map(myFunction);
function myFunction(value) {
  return value * 2;
}

亲自试一试

Alli kai browsers suka. Array.map()，sai kai Internet Explorer 8 tsa bai tsa.

Hai 9.0 Hai Hai Hai

Array.filter()

filter() Hali hii inakuzalisha mawaka mpya ambao ina mawaka ambao yana kusikitika.

Mfano huu una kuzalisha mawaka mpya kwa thamani za juu ya 18:

实例

var numbers = [45, 4, 9, 16, 25];
var over18 = numbers.filter(myFunction);
function myFunction(value, index, array) {
  return value > 18;
}

亲自试一试

请注意此函数接受 3 个参数：

  • 项目值
  • 项目索引
  • 数组本身

Kwenye mfano huu, hali ya kurekwa haitumie thamani za index na array, kwa hivyo inaweza kuwa inasikitika:

实例

var numbers = [45, 4, 9, 16, 25];
var over18 = numbers.filter(myFunction);
function myFunction(value) {
  return value > 18;
}

亲自试一试

Alli kai browsers suka. Array.filter()，sai kai Internet Explorer 8 tsa bai tsa.

Hai 9.0 Hai Hai Hai

Array.reduce()

reduce() Hali hii inafanya kazi kwa hali kwa kila mawaka katika mawaka, kwa kuzalisha (kukadilisha) thamani moja.

reduce() Hali hii inafanya kazi katika mawaka kutoka kushoto hadi kushoto. Tazama na reduceRight().

reduce() Hali hii haikubadilisha mawaka ya asili.

Mfano huu una kufikirisha jumla ya barabara zote katika mawaka:

实例

var numbers1 = [45, 4, 9, 16, 25];
var sum = numbers1.reduce(myFunction);
function myFunction(total, value, index, array) {
  return total + value;
}

亲自试一试

Raba ina hankali ya hali, ina kubadilika 4 thamani:

  • 总数（初始值/先前返回的值）
  • 项目值
  • 项目索引
  • 数组本身

上例并未使用 index 和 array 参数。可以将它改写为：

实例

var numbers1 = [45, 4, 9, 16, 25];
var sum = numbers1.reduce(myFunction);
function myFunction(total, value) {
  return total + value;
}

亲自试一试

reduce() Hali hii inaweza kubadilika thamani ya kuzalishwa:

实例

var numbers1 = [45, 4, 9, 16, 25];
var sum = numbers1.reduce(myFunction, 100);
function myFunction(total, value) {
  return total + value;
}

亲自试一试

Alli kai browsers suka. Array.reduce()，sai kai Internet Explorer 8 tsa bai tsa.

Hai 9.0 Hai Hai Hai

Array.reduceRight()

reduceRight() Hali hii inafanya kazi kwa hali kwa kila mawaka katika mawaka, kwa kuzalisha (kukadilisha) thamani moja.

reduceRight() Hali hii inafanya kazi katika mawaka kutoka kushoto hadi kushoto. Tazama na reduce().

reduceRight() Hali hii haikubadilisha mawaka ya asili.

Mfano huu una kufikirisha jumla ya barabara zote katika mawaka:

实例

var numbers1 = [45, 4, 9, 16, 25];
var sum = numbers1.reduceRight(myFunction);
function myFunction(total, value, index, array) {
  return total + value;
}

亲自试一试

Raba ina hankali ya hali, ina kubadilika 4 thamani:

  • 总数（初始值/先前返回的值）
  • 项目值
  • 项目索引
  • 数组本身

上例并未使用 index 和 array 参数。可以将它改写为：

实例

var numbers1 = [45, 4, 9, 16, 25];
var sum = numbers1.reduceRight(myFunction);
function myFunction(total, value) {
  return total + value;
}

亲自试一试

Alli kai browsers suka. Array.reduceRight()，sai kai Internet Explorer 8 tsa bai tsa.

Hai 9.0 Hai Hai Hai

Array.every()

every() 方法检查所有数组值是否通过测试。

这个例子检查所有数组值是否大于 18：

实例

var numbers = [45, 4, 9, 16, 25];
var allOver18 = numbers.every(myFunction);
function myFunction(value, index, array) {
  return value > 18;
}

亲自试一试

请注意此函数接受 3 个参数：

  • 项目值
  • 项目索引
  • 数组本身

如果回调函数仅使用第一个参数（值）时，可以省略其他参数：

实例

var numbers = [45, 4, 9, 16, 25];
var allOver18 = numbers.every(myFunction);
function myFunction(value) {
  return value > 18;
}

亲自试一试

Alli kai browsers suka. Array.every()，sai kai Internet Explorer 8 tsa bai tsa.

Hai 9.0 Hai Hai Hai

Array.some()

some() 方法检查某些数组值是否通过了测试。

这个例子检查某些数组值是否大于 18：

实例

var numbers = [45, 4, 9, 16, 25];
var someOver18 = numbers.some(myFunction);
function myFunction(value, index, array) {
  return value > 18;
}

亲自试一试

请注意此函数接受 3 个参数：

  • 项目值
  • 项目索引
  • 数组本身

Alli kai browsers suka. Array.some()，sai kai Internet Explorer 8 tsa bai tsa.

Hai 9.0 Hai Hai Hai

Array.indexOf()

indexOf() Method a na kai a na kai a na kara a na kai a na kara a na kai a na kara a na kai a na kara a na kai a na kara.

Tsan:A na kai a na kara a na kai a na kara a na kai a na kara 0, a na kai a na kara a na kai a na kara a na kai a na kara 1, amma kai kai.

实例

A na kai a na yin a na kara "Apple":

var fruits = ["Apple", "Orange", "Apple", "Mango"];
var a = fruits.indexOf("Apple");

亲自试一试

Alli kai browsers suka. Array.indexOf()，sai kai Internet Explorer 8 tsa bai tsa.

Hai 9.0 Hai Hai Hai

语法

array.indexOf(item, kai)
item dabara. A na kai a kara. A na kai a na yin a kara.
kai dabara. A na kai a kara a na kai a na kara. Negi kai a na kai a na kara kai a na kai a na kara a na kai a na kara.

Kai a na kai a na kara wuri,Array.indexOf() A na kai a na kai a na kara -1.

Kai a na kai a na kara wuri, a na kai a na kara a na kai a na kara.

Array.lastIndexOf()

Array.lastIndexOf() wa Array.indexOf() Dabara, amma dake kai a na kai a na kara a na kai a na kara.

实例

A na kai a na yin a na kara "Apple":

var fruits = ["Apple", "Orange", "Apple", "Mango"];
var a = fruits.lastIndexOf("Apple");

亲自试一试

Alli kai browsers suka. Array.lastIndexOf()，sai kai Internet Explorer 8 tsa bai tsa.

Hai 9.0 Hai Hai Hai

语法

array.lastIndexOf(item, kai)
item dabara. A na kai a kara. A na kai a na yin a kara.
kai 可选。从哪里开始搜索。负值将从结尾开始的给定位置开始，并搜索到开头。

Array.find()

find() 方法返回通过测试函数的第一个数组元素的值。

这个例子查找（返回）大于 18 的第一个元素的值：

实例

var numbers = [4, 9, 16, 25, 29];
var first = numbers.find(myFunction);
function myFunction(value, index, array) {
  return value > 18;
}

亲自试一试

请注意此函数接受 3 个参数：

  • 项目值
  • 项目索引
  • 数组本身

老旧的浏览器不支持 Array.find()。下面列出了完全支持此方法的首个浏览器版本：

45 12 25 8 32

Array.findIndex()

findIndex() 方法返回通过测试函数的第一个数组元素的索引。

这个例子查找大于 18 的第一个元素的索引：

实例

var numbers = [4, 9, 16, 25, 29];
var first = numbers.findIndex(myFunction);
function myFunction(value, index, array) {
  return value > 18;
}

亲自试一试

请注意此函数接受 3 个参数：

  • 项目值
  • 项目索引
  • 数组本身

老旧的浏览器不支持 Array.findIndex()。下面列出了完全支持此方法的首个浏览器版本：

45 12 25 8 32