JavaScript |检查变量是否为字符串

可以使用typeof运算符检查变量的类型。它直接应用于变量名或变量。

句法：

typeof varName;

• varName：变量名。

示例 1：此示例检查变量boolValue和numValue是否为字符串。

  

    
        Javascript | Check if a variable is a string
    

  

  
      
            GeeksForGeeks  
        
    
        var boolValue = true;
         var numValue = 17;
    
  
    
        Click to check
    
    
    
    
        function Geeks() {
            
            <!-- "boolean" value. -->
            var boolValue = true;
              
            <!-- "integer " value. -->
            var numValue = 17;
            var el = 
                document.getElementById("GFG_P");
            var bool, num;
            
            if (typeof boolValue == "string") {
                bool = "is a string";
            } else {
                bool = "is not a string";
            }
            if (typeof numValue == "string") {
                num = "is a string";
            } else {
                num = "is not a string";
            }
            el.innerHTML = "boolValue " + bool 
            + "<br>numValue " + num;
  
        }
    

  

输出：

• 在点击按钮之前：
  
• 点击按钮后：
  

示例 2：此示例检查变量strValue和objGFG是否为字符串。

  

    
        Javascript | Check if a variable is a string
    

  

  
      
            GeeksForGeeks  
        
    
        
        var strValue = 
      "This is GeeksForGeeks";
         
      
      var objGFG = new String( 
      "This is GeeksForGeeks" );
    
  
    
        Click to check
    
    
    
    
        function Geeks() {
            var strValue = "This is GeeksForGeeks";
            var objGFG = new String("This is GeeksForGeeks");
            var el = document.getElementById("GFG_P");
            var str, obj;
            if (typeof strValue == 'string') {
                str = "is a string";
            } else {
                str = "is not a string";
            }
            if (typeof objGFG == "string") {
                obj = "is a string";
            } else {
                obj = "is not a string";
            }
            el.innerHTML = "strValue " + str + "<br>objGFG " + obj;
  
        }
    

  

输出：

• 在点击按钮之前：
  
• 点击按钮后：