New Revised Standard Version
Jonathan said, “Far be it from you! If I knew that it was decided by my father that evil should come upon you, would I not tell you?”

Contemporary English Version
"Don't worry," Jonathan said. "If I find out that my father wants to kill you, I'll certainly let you know."

New American Bible
But Jonathan answered: “Not I! If ever I find out that my father is determined to harm you, I will certainly let you know.”

Douay-Rheims Bible
And Jonathan said: Far be this from thee: for if I should certainly know that evil is determined by my father against thee, I could do no otherwise than tell thee.

And Jonathan said: Far be this from thee: for if I should certainly know that evil is determined by my father against thee, I could do no otherwise than tell thee.

then would

1 Samuel 20:38,42 And Jonathan cried again after the boy, saying: Make haste speedily, stand not. And Jonathan's boy gathered up the arrows, and brought them to his master: . . .

1 Samuel 19:2 And Jonathan told David, saying: Saul, my father, seeketh to kill thee: wherefore look to thyself, I beseech thee, in the morning and thou shalt abide in a secret place, and shalt be hid.