如何将 JSON 属性解析为 Typescript 中的 Map 键？

Question

I want to parse JSON property as a Map key. Here is JSON string:

const jsonString = `{
    "DDBProps": {
      "us-east-1": {
        "test": "2",
        "prod": "100"
      },
      "us-west-2": {
        "test": "2",
        "prod": "100"
      }
    },
    "DDBProps2": {
      "us-east-1": {
        "test": "2",
        "prod": "200"
      },
      "us-west-2": {
        "test": "2",
        "prod": "200"
      }
    }
}`

So, I want these "DDBProps", "DDBProps2", ... "DDBPropsX" to be a Map key, and value to be nested Map. Essentially, something like Map<string, Map<string, Map<string, string>>> . I want this nest map structure because I need to get the number (eg "2", "100", "200" in this JSON) based on the input: DDBPropsType, region, stage .

So I declared interfaces:

interface ThroughputMap {
    throughputMappings: Map<string,RegionMap>
}

interface RegionMap {
    regionMappings: Map<string, StageMap>
}

interface StageMap {
    stageMappings: Map<string, string>
}

// parse
const ddbScaleMap: ThroughputMap = JSON.parse(ddbScalingMappingsJson);

However, this doesn't parse the JSON to correct structure:

console.log(ddbScaleMap)
// output below
{
    "DDBProps": {
      "us-east-1": {"test": "2","prod": "100"},
      "us-west-2": {"test": "2","prod": "100"}
    },
    "DDBProps2": {
      "us-east-1": {"test": "2","prod": "200"},
      "us-west-2": {"test": "2","prod": "200"}
    }
}


console.log(ddbScaleMap.throughputMappings) // output undefined

I can't parse property as Map key.

I tried:

const ddbScaleMap = new Map<string, Map<string, Map<string, string>>>(Object.fromEntries(JSON.parse(jsonString)))

This didn't parse correctly in nested value. Meaning, ddbScaleMap.get("DDBProps").get("us-west-2"); .get("us-west-2") cannot be called.

Answer 1

So apparently, there is a way to access nested value easily without converting to a map. In TS, you use keyof typeof to access nested value like this:

function getThroughputByKey(key: string, region: string, stage: string): number {
    const defaultThroughputValue = 1;

    const regionToStageMap = ddbScalingMappingsObject[key as keyof typeof ddbScalingMappingsObject];
    const stageToThroughputMap = regionToStageMap[region as keyof typeof regionToStageMap];
    const throughputString = stageToThroughputMap[stage as keyof typeof stageToThroughputMap];
    const throughput = Number(throughputString);

    return throughput || defaultThroughputValue;
}