Uses the query function of DynamoDB DocumentClient class to count all the items from a table. Use index with only keys projected for best performance.

dynamo_db_query_all_items_count.js

const AWS = require("aws-sdk");

const documentClient = new AWS.DynamoDB.DocumentClient();

let itemCount = 0;

var params = {
    TableName: 'table_name',
    IndexName: 'part-range-index',
    KeyConditionExpression: '#t = :hkey',
    ExpressionAttributeNames: { "#t": "type" },
    ExpressionAttributeValues: { ':hkey': 'Solution' },
    Limit: 1000,
    Select: 'COUNT'
};

const onScan = (err, data) => {
    if (err) {
        console.log(err);
        console.log(`Total items found ${itemCount}`);

    } else {
        if (data) {
            itemCount += data.Count;

            if ('LastEvaluatedKey' in data) {
                params.ExclusiveStartKey = data.LastEvaluatedKey;
                documentClient.query(params, onScan);

            } else {
                console.log(`COMPLETE!! Total Iems found ${itemCount}`);
            }
        }
    }
}

documentClient.query(params, onScan);