How to use a string condition to filter a list of objects in Javascript?

Question

How to use a string condition to filter a list of objects in Javascript?

Below is the structure of the object:

var objList = [
    { "age": 19, "valueField": 34, "booleanField": false },
    { "age": 15, "valueField": 5,  "booleanField": false },
    { "age": 22, "valueField": 17, "booleanField": true }
];

Given the condition below:

var condition = 'age > 18 && age < 30 && booleanField == true';

A filter function can be used as shown here:

var newObjList = objList.filter(function(obj) {
    return obj.age > 18 && obj.age < 30 && obj.booleanField == true;
});

However, it's desired to use the condition directly without prefixing "obj." to each field.

objList.filter(function(obj) {
    return conditon; // all the fields referenced in the condition should point to the corresponding obj fields
})

This approach resembles a SQL query:

SELECT * 
FROM objlist
where " + condition + ";

The question arises: Is this achievable?

javascript filter implicit

Answer 1

Answer №1

To create a new function callback, you can replace all existing keys within the object in condition with a specific suffix and update the return statement accordingly.

It may be necessary to add padding to the keys for replacement in order to avoid replacing unintended substrings.

var array = [{ age: 19, valueField: 34, booleanField: false }, { age: 15, valueField: 5, booleanField: false }, { age: 22, valueField: 17, booleanField: true }];
    condition = 'age > 18 && age < 30 && booleanField == true',
    cb = new Function('o', 'return ' + condition.replace(new RegExp(Object.keys(array[0]).join('|'), 'g'), 'o.$&'));

console.log(array.filter(cb));

Answer 2

To create a new function callback, you can replace all existing keys within the object in condition with a specific suffix and update the return statement accordingly.

It may be necessary to add padding to the keys for replacement in order to avoid replacing unintended substrings.

var array = [{ age: 19, valueField: 34, booleanField: false }, { age: 15, valueField: 5, booleanField: false }, { age: 22, valueField: 17, booleanField: true }];
    condition = 'age > 18 && age < 30 && booleanField == true',
    cb = new Function('o', 'return ' + condition.replace(new RegExp(Object.keys(array[0]).join('|'), 'g'), 'o.$&'));

console.log(array.filter(cb));

Answer 3

Answer №2

Important Note:

I want to highlight at the beginning that the solution provided involves using both with and eval, which should be approached with extreme caution (only use them if you are absolutely certain that the condition string does not contain any sort of harmful code).

Here is the Solution:

To achieve this functionality, you can utilize eval along with with in the following manner:

var newObjList = objList.filter(function(obj) {
    return eval("with(obj) {" + condition + "}");
});

For Example:

var objList = [ { "age": 19, "valueField": 34, "booleanField": false }, { "age": 15, "valueField": 5,  "booleanField": false }, { "age": 22, "valueField": 17, "booleanField": true } ];
var condition = 'age > 18 && age < 30 && booleanField == true';

var newObjList = objList.filter(function(obj) {
    return eval("with(obj) {" + condition + "}");
});

console.log(newObjList);

Answer 4

Important Note:

I want to highlight at the beginning that the solution provided involves using both with and eval, which should be approached with extreme caution (only use them if you are absolutely certain that the condition string does not contain any sort of harmful code).

Here is the Solution:

To achieve this functionality, you can utilize eval along with with in the following manner:

var newObjList = objList.filter(function(obj) {
    return eval("with(obj) {" + condition + "}");
});

For Example:

var objList = [ { "age": 19, "valueField": 34, "booleanField": false }, { "age": 15, "valueField": 5,  "booleanField": false }, { "age": 22, "valueField": 17, "booleanField": true } ];
var condition = 'age > 18 && age < 30 && booleanField == true';

var newObjList = objList.filter(function(obj) {
    return eval("with(obj) {" + condition + "}");
});

console.log(newObjList);

How to use a string condition to filter a list of objects in Javascript?

Answer №1

Answer №2

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