React.createElement 代码片段

export function createElement(type, config, children) {
    let propName;

    // Reserved names are extracted
    const props = {};

    let key = null;
    let ref = null;
    let self = null;
    let source = null;

    if (config != null) {
        if (hasValidRef(config)) {
            ref = config.ref;

            if (__DEV__) {
                warnIfStringRefCannotBeAutoConverted(config);
            }
        }
        if (hasValidKey(config)) {
            key = '' + config.key;
        }

        self = config.__self === undefined ? null : config.__self;
        source = config.__source === undefined ? null : config.__source;
        // Remaining properties are added to a new props object
        for (propName in config) {
            if (
                hasOwnProperty.call(config, propName) &&
                !RESERVED_PROPS.hasOwnProperty(propName)
            ) {
                props[propName] = config[propName];
            }
        }
    }

    // Children can be more than one argument, and those are transferred onto
    // the newly allocated props object.
    const childrenLength = arguments.length - 2;
    if (childrenLength === 1) {
        props.children = children;
    } else if (childrenLength > 1) {
        const childArray = Array(childrenLength);
        for (let i = 0; i < childrenLength; i++) {
            childArray[i] = arguments[i + 2];
        }
        if (__DEV__) {
            if (Object.freeze) {
                Object.freeze(childArray);
            }
        }
        props.children = childArray;
    }

    // Resolve default props
    if (type && type.defaultProps) {
        const defaultProps = type.defaultProps;
        for (propName in defaultProps) {
            if (props[propName] === undefined) {
                props[propName] = defaultProps[propName];
            }
        }
    }
    if (__DEV__) {
        if (key || ref) {
            const displayName =
                typeof type === 'function'
                    ? type.displayName || type.name || 'Unknown'
                    : type;
            if (key) {
                defineKeyPropWarningGetter(props, displayName);
            }
            if (ref) {
                defineRefPropWarningGetter(props, displayName);
            }
        }
    }
    // 输出
    // type 标签类型 例如 div,p,span
    // key(diff时使用)
    // ref(为了操作真实dom)
    // self 自身
    return ReactElement(
        type,
        key,
        ref,
        self,
        source,
        ReactCurrentOwner.current,
        props,
    );
}