在js的数据json中如何判断某个元素是否存在

setProductArray(index) {
	const that = this;
	let data = that.productList[that.menuSelect].child_product_list[index];
	if (that.productArray.length) {
		let isSetIndex = that.productArray.findIndex(item => item.id === data.id);
		if(isSetIndex == -1){
			hat.productArray.push(data);
		}else{
			that.productArray[isSetIndex].number++;
		}
	 else {
		that.productArray.push(data);
	 }
},