make form.submit return a promise

[hvsy]

参考以下示例,当form 的 submit 方法返回一个 promise 对象的时候. 用户可以很方便的实现以下需求

1. 防止重复提交

2. 显示表单正在提交中

const AsyncButton = (props)=>{
    const {onClick,children} = props;
    const [ing,setIng] = useState(false);
    return <a onClick={async()=>{
            if(ing) return;
            setIng(true);
            try{
                await onClick();
            }finally{
                setIng(false);
            }
    }}>
        {children}
    </a>
};
const TestComponent = ()=>{
    const form = useForm();
    return <div>
        <Form onFinish={(values)=>{
            return axios.post("...",values);
        }}>
            ...
        </Form>
        <AsyncButton
        onClick={()=>{
            return form.submit();
        }}
        >
                submit
        </AsyncButton>
    </div>
};

[codecov[bot]]

Codecov Report

Merging #187 into master will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #187   +/-   ##
=======================================
  Coverage   99.89%   99.89%           
=======================================
  Files          13       13           
  Lines         912      915    +3     
  Branches      208      207    -1     
=======================================
+ Hits          911      914    +3     
  Misses          1        1           

Impacted Files	Coverage Δ
src/Form.tsx	100.00% <100.00%> (ø)
src/useForm.ts	99.71% <100.00%> (+<0.01%)	:arrow_up:

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[shaodahong]

https://github.com/react-component/field-form/pull/108#issuecomment-608241087

[HHHui]

急需一个submitting状态。。