Adding conditions to filter() dynamically in Javascript

Question

I want to add conditions in JavaScript filter() method dynamically.

I have the code below:

let condition = '';
let a = ['empEmail', 'employeeAction', 'transactionNo', 'deviceListName', 'projectName'];

if (this.selectedEmployeeAlias != undefined) {
  condition += '&& a => a.empEmail === this.selectedEmployeeAlias';
}
if (this.employeeStatusList != undefined) {
  condition += '&& a.employeeAction === this.employeeStatusList'
}
if (this.selectedTransactionNo != undefined) {
  condition += '&& a.transactionNo === this.selectedTransactionNo';
}
if (this.selectedDeviceList != undefined) {
  condition += ' && a.deviceListName == this.selectedDeviceList';
}
if (this.selectedProjectName != undefined) {
  condition += '&& a.projectName == this.selectedProjectName';
}

var finalCondition = condition.substring(2, condition.length);
var fArray = arrayDetails.filter(finalCondition);

The code is returning an error as:

finalCondition is not a function.

Could you please let me know how can I add conditions to filter() dynamically.

Its because "finalCondition" is a string returned by "substring", the filter routine is expecting a function to be passed to it. See w3schools.com/jsref/jsref_filter.asp — SPlatten
– SPlatten, Commented Jul 4, 2018 at 10:49
please add the sample data, you have and what this is pointing to. — Nina Scholz
– Nina Scholz, Commented Jul 4, 2018 at 10:58

Nina Scholz · Accepted Answer · 2018-07-04 11:13:11Z

2

You could take an array of functions with conditions. Then iterate with every.

var conditions = [];

if (this.selectedEmployeeAlias !== undefined) {
    conditions.push(a => a.empEmail === this.selectedEmployeeAlias);
}
if (this.employeeStatusList !== undefined) {
    conditions.push(a => a.employeeAction === this.employeeStatusList);
}
if (this.selectedTransactionNo !== undefined) {
    conditions.push(a => a.transactionNo === this.selectedTransactionNo);
}
if (this.selectedDeviceList !== undefined) {
    conditions.push(a => a.deviceListName == this.selectedDeviceList);
}
if (this.selectedProjectName !== undefined) {
    conditions.push(a => a.projectName == this.selectedProjectName);
}

var fArray = arrayDetails.filter(o => conditions.every(c => c(o)));

edited Jul 4, 2018 at 11:13

answered Jul 4, 2018 at 10:56

Nina Scholz

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2 Comments

Jonas Wilms Over a year ago

Omitting != undefined seems dangerous. What if its 0 or false or ...

Nina Scholz Over a year ago

right, the properties could contains numbers and empty strings, or what ever falsy values.

Jonas Wilms · Accepted Answer · 2018-07-04 11:10:38Z

0

As you got the nakes of the keys, just loop over them and check for undefineds:

const keys = ['empEmail', 'employeeAction', 'transactionNo', 'deviceListName', 'projectName'];

const result = arrayDetails.filter(el => {
   for(const key of keys) {
     if(this[key] === undefined) continue;
     if(this[key] !== el[key]) return false;
   }
   return true;
});

answered Jul 4, 2018 at 11:10

Jonas Wilms

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Comments

andria_girl · Accepted Answer · 2018-07-04 11:05:34Z

`eval` to the Rescue!

While it's generally advised against, eval does exactly what you want here.

Just pass your condition variable to eval inside the .filter method and voila!

let condition='';
let a = ['empEmail', 'employeeAction', 'transactionNo', 'deviceListName', 'projectName'];

if (this.selectedEmployeeAlias != undefined) {                    
  condition += '&& a => a.empEmail === this.selectedEmployeeAlias';
}
if (this.employeeStatusList != undefined) {
  condition += '&& a.employeeAction === this.employeeStatusList'
}
if (this.selectedTransactionNo != undefined) {
  condition += '&& a.transactionNo === this.selectedTransactionNo';
}
if (this.selectedDeviceList != undefined) {
  condition += ' && a.deviceListName == this.selectedDeviceList';
}
if (this.selectedProjectName != undefined) {
  condition += '&& a.projectName == this.selectedProjectName';
}

var finalCondition=condition.substring(2, condition.length);
var fArray=arrayDetails.filter(stuff => eval(finalCondition));

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