index.js
function extend(source, target, deep) {
    if (deep) {
        return lodash.merge(lodash.cloneDeep(source), target);
    } else {
        return lodash.assignIn(source, target);
    }
}
function extend(source, target, deep) {
    if (deep) {
        return lodash.merge(lodash.cloneDeep(source), target);
    } else {
        return lodash.assignIn(source, target);
    }
}
function extend ( source , target , deep ) { if ( deep ) { return lodash . merge ( lodash . cloneDeep ( source ) , target ) ; } else { return lodash . assignIn ( source , target ) ; } }
So that the target object inherits the source,
deep depth is true depth inheritance
@param {any} source
@param {any} target
@param {any} deep
@returns {*}
So that the target object inherits the source deep depth is true depth inheritance