String and variable are spliced into variable name

Record a little bit of knowledge

eval() The use of functions

eval() MDN Document introduction

 var ab = ' I'm Trump ';
    var c = 'b'
    var d = eval('a' + c);
    console.log('a'+c);      //  Output  ab
    console.log(d)           //  Output   I'm Trump 

notes ： go through MDN file The introduction shows that eval() A global function , Use has certain advantages and disadvantages