introduce
This article mainly introduces judging whether there is an element in the array, and returning all elements that meet the conditions; judging whether there is an element that meets the conditions in the Object in the array, and returning all There is a key (key); judge whether there is an element that satisfies the condition in the Object, judge whether there is a key (key) in the Object, and return all the keys (keys) in the Object
1. The elements in the array are number and string
1. Determine whether an element exists in the array
Example: arr=[1,2,3,4];
JS method:
arr.indexOf(3) > -1; // true
arr.indexOf(9) > -1; // false
2. Determine whether there is an element that satisfies the condition in the array, and return all elements that meet the condition
Example: filter all odd numbers in the array: arr=[1, 2, 3, 4, 5, 6, 7, 8, 9];
JS method:
const list = arr.filter(item => item % 2 === 1);
console.log(list); // [ 1, 3, 5, 7, 9 ]
two, object
1. Determine whether there is an element that satisfies the condition in Object
example:
obj = {
name:'李四', sex:'男', age:22};
JS method:
obj.name === '张三'; // true
obj.name === '王五'; // false
2. Determine whether a key (key) exists in the Object
example:
obj = {
name:'张三', sex:'男'};
JS method:
方法1：
Object.hasOwnProperty.call(obj,'name'); // true
Object.hasOwnProperty.call(obj,'age'); // false
方法2：
obj.hasOwnProperty('name'); // true
obj.hasOwnProperty('age'); // false
方法3：
'name' in obj; // true
'age' in obj; // false
3. Return all keys (keys) in Object
example:
obj = {
name:'张三', sex:'男'};
JS method:
方法1：
Object.getOwnPropertyNames(obj); // [ 'name', 'sex' ]
方法2：
Object.keys(obj); // [ 'name', 'sex' ]
3. The elements in the array are object
1. Determine whether there is an element that satisfies the condition in the Object in the array
example:
arr = [
{
name:'张三', sex:'男', age:11},
{
name:'李四', sex:'男', age:22},
];
JS method:
arr.some(item => item.name === '张三'); // true
arr.some(item => item.name === '王五'); // false
2. Determine whether there is an element that satisfies the condition in the Object in the array, and return all elements that meet the condition
example:
arr = [
{
name:'张三', sex:'男', age:11},
{
name:'李四', sex:'男', age:22},
{
name:'王五', sex:'男', age:33},
];
JS method:
const list = arr.filter(item => item.age === 11);
console.log(list); // [{ name: '张三', sex: '男', age: 11 },{ name: '王五', sex: '男', age: 11 }]
3. Determine whether a key (key) exists in the Object in the array
example:
arr = [
{
name:'张三', sex:'男'},
{
name:'李四', sex:'男'},
{
name:'王五', sex:'男'},
];
JS method:
方法1：
arr.some(item=>Object.hasOwnProperty.call(item,'name')); // true
arr.some(item=>Object.hasOwnProperty.call(item,'age')); // false
方法2：
arr.some(item=>item.hasOwnProperty('name')); // true
arr.some(item=>item.hasOwnProperty('age')); // false
方法3：
arr.some(item=>'name' in item); // true
arr.some(item=>'age' in item); // false
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