change value of one field on the basis of other using spfx field customizer

Hi LaxmikantB2 

If you are using SPFx Field Customizer, then implement the onRenderCell with below logic

The method has signature as follows:

public onRenderCell(event: IFieldCustomizerCellEventParameters): void 

Use below code to get the Security field value:

const securityValue = event.listItem["_values"].get("Security");

Once you get the item id, you can get the value of other field from same item. 

Return the value as:

event.domElement.innerHTML = `<div>${securityValue}</div>`