Below example shows how to change the hyperlink for "ID" and "Title(LinkTitle)" field inside the list view using CSR.

Step1 : Create a JS file and paste below code

(function () {
    
    function registerRenderer() {
        var ctxForm = {};
        ctxForm.Templates = {};

        ctxForm.Templates = {
            Fields : {
                'LinkTitle': { //------ Change Hyperlink of LinkTitle
                    View : function (ctx) {
                        var url = String.format('{0}?ID={1}', "/sites/Lists/testlist/EditItem.aspx", ctx.CurrentItem.ID);
                        return String.format('<a href="{0}" onclick="EditItem2(event, \'{0}\');return false;">{1}</a>', url, ctx.CurrentItem.Title);
                    }
                },
                'ID' : { //------ Change Hyperlink from ID field
                    View : function (ctx) {
                        var url = String.format('{0}?ID={1}', "/IssueTracker/Lists/testlist/DisplayItem.aspx", ctx.CurrentItem.ID);
                        return String.format('<a href="{0}" onclick="EditItem2(event, \'{0}\');return false;">{1}</a>', url, ctx.CurrentItem.ID);
                    }
                },

            }
        };
        SPClientTemplates.TemplateManager.RegisterTemplateOverrides(ctxForm);
    }
    ExecuteOrDelayUntilScriptLoaded(registerRenderer, 'clienttemplates.js');

})();

Step 2 : GoTo web part properties of List View and add JS Link reference to this newly created js file (e.g. ~sitecollection/SiteAssets/CSRCodeFile.js)

(Note : Refer your JSlink in this format only. "~sitecollection/YourJSfFilePath".)

Step 3 : Appy and Done

This example shows how to hide a "Date" field from the SharePoint list view using CSR.

(function () {
    
    function RemoveFields(ctx) {
        var fieldName = "Date"; // here Date is field or column name to be hide
        var header = document.querySelectorAll("[displayname=" + fieldName + "]")[0].parentNode;
        var index = [].slice.call(header.parentNode.children).indexOf(header) + 1;
        header.style.display = "none";
        for (var i = 0, cells = document.querySelectorAll("td:nth-child(" + index + ")"); i < cells.length; i++) {
            cells[i].style.display = "none";
        }
    }

    function registerRenderer() {
        var ctxForm = {};
        ctxForm.Templates = {};
        ctxForm.OnPostRender = RemoveFields;
        SPClientTemplates.TemplateManager.RegisterTemplateOverrides(ctxForm);
    }
    ExecuteOrDelayUntilScriptLoaded(registerRenderer, 'clienttemplates.js');

})();

Suppose we have a SharePoint list and it has four fields viz. Title, Full Name, Email, Mobile Number etc. Now if you want to apply custom validation in New/Edit Item form, you can easily do it with CSR code. The below mentioned can validate following conditions in forms:

• Blank values in fields
• Email id format check with regular expression
• Mobile Number format Check with regular expression
• Full Name field should not contain numeric values

Step : 1 Create a JS file, say CSRValidations.js and copy paste following code in the JS file

        (function () { 
     
        // Create object that have the context information about the field that we want to change it's output render  
        var fieldContext = {}; 
        fieldContext.Templates = {}; 
        fieldContext.Templates.Fields = { 
            // Apply the new rendering for Email field on New and Edit Forms 
            "Title": { 
                "NewForm": titleFieldTemplate, 
                "EditForm":  titleFieldTemplate
            },
            "Full_x0020_Name": { 
                "NewForm": fullNameFieldTemplate, 
                "EditForm":  fullNameFieldTemplate
            },
            "Email": { 
                "NewForm": emailFieldTemplate, 
                "EditForm":  emailFieldTemplate 
            },
            "Mobile_x0020_Phone": { 
                "NewForm": mobilePhoneFieldTemplate, 
                "EditForm":  mobilePhoneFieldTemplate
            }
        }; 
     
        SPClientTemplates.TemplateManager.RegisterTemplateOverrides(fieldContext); 
     
    })(); 
     
    // This function provides the rendering logic 
    function emailFieldTemplate(ctx) { 
     
        var formCtx = SPClientTemplates.Utility.GetFormContextForCurrentField(ctx); 
     
        // Register a callback just before submit. 
        formCtx.registerGetValueCallback(formCtx.fieldName, function () { 
            return document.getElementById('inpEmail').value; 
        }); 
     
        //Create container for various validations 
        var validators = new SPClientForms.ClientValidation.ValidatorSet(); 
        validators.RegisterValidator(new emailValidator()); 
     
        // Validation failure handler. 
        formCtx.registerValidationErrorCallback(formCtx.fieldName, emailOnError); 
     
        formCtx.registerClientValidator(formCtx.fieldName, validators); 
     
        return "<span dir='none'><input type='text' value='" + formCtx.fieldValue + "'  maxlength='255' id='inpEmail' class='ms-long'> \ <br><span id='spnEmailError' class='ms-formvalidation ms-csrformvalidation'></span></span>"; 
    } 
     
    // Custom validation object to validate email format 
    emailValidator = function () { 
        emailValidator.prototype.Validate = function (value) { 
            var isError = false; 
            var errorMessage = ""; 
     
            //Email format Regex expression 
            //var emailRejex = /\S+@\S+\.\S+/; 
            var emailRejex = /^(([^<>()[\]HYPERLINK "\\.,;:\s@\"\\.,;:\s@\"]+(\.[^<>()[\]HYPERLINK "\\.,;:\s@\"\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
    
            if (value.trim() == "") { 
                isError = true; 
                errorMessage = "You must specify a value for this required field.";
            }else if (!emailRejex.test(value) && value.trim()) {
                isError = true;
                errorMessage = "Please enter valid email address";
            } 
     
            //Send error message to error callback function (emailOnError) 
            return new SPClientForms.ClientValidation.ValidationResult(isError, errorMessage); 
        }; 
    }; 
     
    // Add error message to spnError element under the input field element 
    function emailOnError(error) { 
        document.getElementById("spnEmailError").innerHTML = "<span role='alert'>" + error.errorMessage + "</span>"; 
    } 
    
    // This function provides the rendering logic 
    function titleFieldTemplate(ctx) { 
     
        var formCtx = SPClientTemplates.Utility.GetFormContextForCurrentField(ctx);
        // Register a callback just before submit.             
        
        formCtx.registerGetValueCallback(formCtx.fieldName, function () { 
            return document.getElementById('inpTitle').value; 
        }); 
     
        //Create container for various validations 
        var validators = new SPClientForms.ClientValidation.ValidatorSet(); 
        validators.RegisterValidator(new titleValidator()); 
     
        // Validation failure handler. 
        formCtx.registerValidationErrorCallback(formCtx.fieldName, titleOnError); 
     
        formCtx.registerClientValidator(formCtx.fieldName, validators); 
     
        return "<span dir='none'><input type='text' value='" + formCtx.fieldValue + "'  maxlength='255' id='inpTitle' class='ms-long'> \ <br><span id='spnTitleError' class='ms-formvalidation ms-csrformvalidation'></span></span>"; 
    } 
     
    // Custom validation object to validate title format 
    titleValidator = function () { 
        titleValidator.prototype.Validate = function (value) { 
            var isError = false; 
            var errorMessage = ""; 
    
            if (value.trim() == "") { 
                isError = true; 
                errorMessage = "You must specify a value for this required field.";
            }
     
            //Send error message to error callback function (titleOnError) 
            return new SPClientForms.ClientValidation.ValidationResult(isError, errorMessage); 
        }; 
    }; 
     
    // Add error message to spnError element under the input field element 
    function titleOnError(error) { 
        document.getElementById("spnTitleError").innerHTML = "<span role='alert'>" + error.errorMessage + "</span>"; 
    } 
    
    // This function provides the rendering logic 
    function mobilePhoneFieldTemplate(ctx) { 
     
        var formCtx = SPClientTemplates.Utility.GetFormContextForCurrentField(ctx); 
     
        // Register a callback just before submit. 
        formCtx.registerGetValueCallback(formCtx.fieldName, function () { 
            return document.getElementById('inpMobilePhone').value; 
        }); 
     
        //Create container for various validations 
        var validators = new SPClientForms.ClientValidation.ValidatorSet(); 
        validators.RegisterValidator(new mobilePhoneValidator()); 
     
        // Validation failure handler. 
        formCtx.registerValidationErrorCallback(formCtx.fieldName, mobilePhoneOnError); 
     
        formCtx.registerClientValidator(formCtx.fieldName, validators); 
     
        return "<span dir='none'><input type='text' value='" + formCtx.fieldValue + "'  maxlength='255' id='inpMobilePhone' class='ms-long'> \ <br><span id='spnMobilePhoneError' class='ms-formvalidation ms-csrformvalidation'></span></span>"; 
    } 
     
    // Custom validation object to validate mobilePhone format 
    mobilePhoneValidator = function () { 
        mobilePhoneValidator.prototype.Validate = function (value) { 
            var isError = false; 
            var errorMessage = ""; 
     
            //MobilePhone format Regex expression 
            //var mobilePhoneRejex = /\S+@\S+\.\S+/; 
            var mobilePhoneRejex = /^[0-9]+$/;
    
            if (value.trim() == "") { 
                isError = true; 
                errorMessage = "You must specify a value for this required field.";
            }else if (!mobilePhoneRejex.test(value) && value.trim()) {
                isError = true;
                errorMessage = "Please enter valid mobile phone number";
            } 
     
            //Send error message to error callback function (mobilePhoneOnError) 
            return new SPClientForms.ClientValidation.ValidationResult(isError, errorMessage); 
        }; 
    }; 
     
    // Add error message to spnError element under the input field element 
    function mobilePhoneOnError(error) { 
        document.getElementById("spnMobilePhoneError").innerHTML = "<span role='alert'>" + error.errorMessage + "</span>"; 
    } 
    
    // This function provides the rendering logic 
    function fullNameFieldTemplate(ctx) { 
     
        var formCtx = SPClientTemplates.Utility.GetFormContextForCurrentField(ctx); 
     
        // Register a callback just before submit. 
        formCtx.registerGetValueCallback(formCtx.fieldName, function () { 
            return document.getElementById('inpFullName').value; 
        }); 
     
        //Create container for various validations 
        var validators = new SPClientForms.ClientValidation.ValidatorSet(); 
        validators.RegisterValidator(new fullNameValidator()); 
     
        // Validation failure handler. 
        formCtx.registerValidationErrorCallback(formCtx.fieldName, fullNameOnError); 
     
        formCtx.registerClientValidator(formCtx.fieldName, validators); 
     
        return "<span dir='none'><input type='text' value='" + formCtx.fieldValue + "'  maxlength='255' id='inpFullName' class='ms-long'> \ <br><span id='spnFullNameError' class='ms-formvalidation ms-csrformvalidation'></span></span>"; 
    } 
     
    // Custom validation object to validate fullName format 
    fullNameValidator = function () { 
        fullNameValidator.prototype.Validate = function (value) { 
            var isError = false; 
            var errorMessage = ""; 
     
            //FullName format Regex expression 
            var fullNameRejex = /^[a-z ,.'-]+$/i;
    
            if (value.trim() == "") { 
                isError = true; 
                errorMessage = "You must specify a value for this required field.";
            }else if (!fullNameRejex.test(value) && value.trim()) {
                isError = true;
                errorMessage = "Please enter valid name";
            } 
     
            //Send error message to error callback function (fullNameOnError) 
            return new SPClientForms.ClientValidation.ValidationResult(isError, errorMessage); 
        }; 
    }; 
     
    // Add error message to spnError element under the input field element 
    function fullNameOnError(error) { 
        document.getElementById("spnFullNameError").innerHTML = "<span role='alert'>" + error.errorMessage + "</span>"; 
    } 

Step : 2 Open New Item Form in browser. Edit page and edit web part.

Step : 3 In Web part properties, Go to Miscellaneous --> JS link --> paste the path of your js file (e.g. ~sitecollection/SiteAssets/CSRValidations.js)

Step : 4 Save Web part properties and page.

There are cases when you need to change Display Name of column in a list view

e.g. Column Name showing in the view is "IsApprovalNeeded" and you want to appear as "Is Approval Needed?".

You can, of course change the display name of a column by changing the column title in list settings, but if you want to keep it as it is in the list settings and only modify it on the page preview then you can do it by using CSR(Client-Side-Rendering).

Here is the code...

(function () {    

    function preTaskFormRenderer(renderCtx) {
       modifyColumns(renderCtx);       
    }

    function modifyColumns(renderCtx)
    {
      var arrayLength= renderCtx.ListSchema.Field.length;
        for (var i=0; i < arrayLength;i++)
        {
           if(renderCtx.ListSchema.Field[i].DisplayName == 'IsApprovalNeeded')
             {
               var newTitle= "Is Approval Needed?";
               var linkTitleField = renderCtx.ListSchema.Field[i];
               linkTitleField.DisplayName = newTitle;
             }
         }
    }
    
    function registerRenderer()
    {
      var ctxForm = {};
      ctxForm.Templates = {};
      ctxForm.OnPreRender = preTaskFormRenderer;
      SPClientTemplates.TemplateManager.RegisterTemplateOverrides(ctxForm);
    }

    ExecuteOrDelayUntilScriptLoaded(registerRenderer, 'clienttemplates.js');

})();