Spread Operator
序言
本周在写分页查询的时候遇到了关于...
运算符的问题,想到之前例会提过这个运算符,但是当自己独立使用时还是会遇到问题。
分页查询
查询条件:name
export class TeacherIndexComponent implements OnInit {pageable = new Pageable();
loading = true;
isOkLoading = false;
teachers = new Array();
teacherPage = new Page();
params: Params;
nameFormControl = new FormControl('');
constructor(private teacherService: TeacherService,
private systemConfig: SystemConfigService,
private route: ActivatedRoute) {
}// 初始化
ngOnInit() {
this.route.queryParams.subscribe((params: {page?: string, size?: string}) => {
this.nameFormControl.setValue(params['name']);
this.reload(params);
});
}onSubmit(): void {
const name = this.nameFormControl.value;
this.reload({...this.params, ...{name}});
}/**
* 查询
* @param params page: 当前页 size: 每页大小
*/
reload(params: Params): void {
// 发起查询params
this.params = params;
this.teacherService.pageByName(
// 调用stringToIntegerNumber将查询的字符串转为number
getDefaultWhenValueIsInValid(params['page'], '0'),
getDefaultWhenValueIsInValid(params['size'], this.systemConfig.getPageSize()),
{
name: params['name'],
},
).subscribe(page => {
this.teacherPage = page;
});
}/**
* 点击分页
* @param page 当前页
*/
onPageChange(page: number): void {
this.reload({...this.params, ...{page}});
}/**
* 点击改变每页大小
* @param size 每页大小
*/
onSizeChange(size: number): void {
this.reload({...this.params, ...{size}});
}
}
这是正确代码,但是当我将 onSubmit()方法改成如下:
onSubmit(): void {
// 将{name}直接改成this.nameFormControl.value
this.reload({...this.params, ...this.nameFormControl.value});
}
此时如果nameFormControl.value为'name',那么在控制台打印的结果就是:
![Spread Operator](https://img.it610.com/image/info9/285df3d7abf14ee6b490eb6a0453aab6.jpg)
文章图片
将一个
‘name’
字符串直接变成一个数组对象?踩坑记录
此时当我使用param['name]时,获取到的恒为undefined,不断打断点之后发现错误所在。
对比其他写法:{...this.params, ...{xxx}}
猜测:
const name1 = 'name';
console.log({name1});
// 打印结果是{name1: 'name'}
结果:
![Spread Operator](https://img.it610.com/image/info9/e37df07f5c264e36b2f783a75e7eaced.jpg)
文章图片
Spread Operator
何为扩展操作符呢? The main objective of the spread operator is to spread the elements of an array or object.
简言之:扩展数组或对象元素
【Spread Operator】扩展对象使用
示例一:
const point2D = {x: 1, y: 2};
const anotherPoint3D = {x: 5, z: 4, ...point2D};
console.log(anotherPoint3D);
// {x: 1, y: 2, z: 4}
const yetAnotherPoint3D = {...point2D, x: 5, z: 4}
console.log(yetAnotherPoint3D);
// {x: 5, y: 2, z: 4}
示例二:
const foo = {a: 1, b: 2, c: 0};
const bar = {c: 1, d: 2};
/** Merge foo and bar */
const fooBar = {...foo, ...bar};
// fooBar is now {a: 1, b: 2, c: 1, d: 2}
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