数组元素是未定义的Javascript

Question

The array elements in Bind are undefined even though there is data in bindInfo. Any suggestions.

let bindinfo =
{
    clientid: 1,
    clientname: 'Web Client',
    nowutc: now_utc,
    bindlist: Bindings(this.props.bindDetails)

}
Bindings(bin)
{
    var Bind = [];
    Bind = bin.map(bindItem => {
        var bindInfo;
        bindInfo = {
            bindingid: bindItem.bindId,
            function: bindItem.functionName,
            aggregation: bindItem.aggregation,
            datalimit: bindItem.datalimit
        }
        Bind.push(bindInfo);
    });
    return Bind;
}

Answer 1

After the .map operation completes, bind is assigned to the result of the .map - that is, the element returned on each iteration of .map is the new array elemenet. But you never return anything from the mapper function, so even if you initially push to Bind , your later reassignment of Bind resets it.

Either use .map properly and return the item on each iteration:

const Bind = bin.map(bindItem => {
  return {
    bindingid: bindItem.bindId,
    function: bindItem.functionName,
    aggregation: bindItem.aggregation,
    datalimit: bindItem.datalimit
  };
});

Or (not recommended) use forEach rather than .map , and don't reassign Bind :

const Bind = [];
bin.forEach(bindItem => {
  var bindInfo = {
    bindingid: bindItem.bindId,
    function: bindItem.functionName,
    aggregation: bindItem.aggregation,
    datalimit: bindItem.datalimit
  }
  Bind.push(bindInfo);
});

Use .map when you want to transform one array into another through the result of the call of .map . Otherwise, for generic looping, use forEach .