没有数组时如何使用forEach [JavaScript]

Question

I would like to use forEach in JavaScript.

sentence.forEach(function(value) {--------

When sentence is an array, forEach works properly.

{
    "sentence": [
        {
            "word": [
                {
                    "content": "tell"
                },
                {
                    "content": "me"
                }
            ]
        },
        {
            "word": [
                {
                    "content": "do"
                },
                {
                    "content": "you"
                },
                {
                    "content": "want"
                }
            ]
        }
    ]
}

However, when sentence has only one value and is not an array, forEach doesn't work and it makes error message like this. Uncaught TypeError: sentence.forEach is not a function

{
    "sentence": {
        "word": {
            "content": "hello"
        }
    }
}

I get json object from external API, so I don't know whether sentence has only one value or many values. How can I solve this problem? Could you give me any information or advice?

Answer 1

Make sure you always have an array, and convert it to an array if it isn't. You could do something like the following:

const sentenceArray = Array.isArray(sentence) ? sentence : [sentence];

Then use sentenceArray instead like so:

sentenceArray.forEach(...

Answer 2

You could convert the data to an array with Array#concat if it is no array or keep the array.

[].concat(data).forEach(callback);

For using this approach, you could wrap it in a function getArray .

 const getArray = value => [].concat(value), callback = ({ word }) => getArray(word).forEach(({ content }) => console.log(content)), a = { sentence: [{ word: [{ content: "tell" }, { content: "me" }] }, { word: [{ content: "do" }, { content: "you" }, { content: "want" }] }] }, b = { sentence: { word: { content: "hello" } } }; getArray(a.sentence).forEach(callback); getArray(b.sentence).forEach(callback);

Answer 3

Split your code conditionally

if(Array.isArray(sentence)
{
 //your foreach
}
else
{
 //pick relevant properties from sentence object
}